The results of kinetic isotope determination and computational studies on Noyori-type catalytic systems for the hydrogenation of ketones are presented. The catalysts examined include RuH2(NHCMe2CMe2NH2)(R-binap) and RuH(NHCMe2CMe2NH2)(PPh3)2. These complexes are active catalysts for ketone hydrogenation in benzene without addition of an external base. The kinetic isotope effect (KIE) for catalysis by RuH2(NHCMe2CMe2NH2)(R-binap) was determined to be 2.0 ± (0.1). The calculated KIE for the model system RuH(NHCH2CH2NH2)(PH3)2 was 1.3, which is smaller than the experimentally observed value but does not include tunneling effects. The complex OsH(NHCMe2CMe2NH2)(PPh3)2 is known to display autocatalytic behaviour when it catalyzes the hydrogenation of acetophenone in benzene. Pseudo first-order reaction conditions are obtained via addition of the product alcohol at the beginning of each kinetic experiment. The KIE determined using various combinations of deuterium-labeled gas, alcohol and ketone was found to be 1.1 ± (0.2). DFT calculations were used to explore the effect of the alcohol and the KIE. An induction period is observed at the start of the hydrogenation that is attributed to the formation of an alkoxide complex. A novel, diamine-orchestrated hydrogen-bonding network is proposed based on DFT calculations to explain how the alkoxide is converted back to the active catalyst. The tetradentate complexes trans-RuHCl[PPh2(ortho-C6H4)CH2NHCH2)]2 and RuHCl[PPh2(ortho-C6H4)CH2NHCMe2)]2 are known to be catalysts for the hydrogenation of acetophenone and benzonitrile in toluene when activated by KOtBu/KH. DFT studies were performed and a mechanism is proposed. The calculated rate limiting step for acetone hydrogenation was found to be heterolytic splitting of dihydrogen, which agrees well with experiment. The novel outer-sphere sequential hydrogenation of a CN triple bond and then a C=N double bond is proposed. A mechanism is proposed, which is supported by DFT studies, to explain the selectivity observed in the nucleophilic attack of amines or aziridines on palladium -prenyl phosphines complexes. Calculations on based on a palladium complex with two phosphorus donor ligands indicated that the observed selectivity would not be produced. Using two new model intermediates with either THF or aziridine substituted for a phosphine ligand trans to the unhindered side of the prenyl ligand did predict the experimentally observed selectivity.

The results of kinetic isotope determination and computational studies on Noyori-type catalytic systems for the hydrogenation of ketones are presented. The catalysts examined include RuH2(NHCMe2CMe2NH2)(R-binap) and RuH(NHCMe2CMe2NH2)(PPh3)2. These complexes are active catalysts for ketone hydrogenation in benzene without addition of an external base. The kinetic isotope effect (KIE) for catalysis by RuH2(NHCMe2CMe2NH2)(R-binap) was determined to be 2.0 ± (0.1). The calculated KIE for the model system RuH(NHCH2CH2NH2)(PH3)2 was 1.3, which is smaller than the experimentally observed value but does not include tunneling effects. The complex OsH(NHCMe2CMe2NH2)(PPh3)2 is known to display autocatalytic behaviour when it catalyzes the hydrogenation of acetophenone in benzene. Pseudo first-order reaction conditions are obtained via addition of the product alcohol at the beginning of each kinetic experiment. The KIE determined using various combinations of deuterium-labeled gas, alcohol and ketone was found to be 1.1 ± (0.2). DFT calculations were used to explore the effect of the alcohol and the KIE. An induction period is observed at the start of the hydrogenation that is attributed to the formation of an alkoxide complex. A novel, diamine-orchestrated hydrogen-bonding network is proposed based on DFT calculations to explain how the alkoxide is converted back to the active catalyst. The tetradentate complexes trans-RuHCl[PPh2(ortho-C6H4)CH2NHCH2)]2 and RuHCl[PPh2(ortho-C6H4)CH2NHCMe2)]2 are known to be catalysts for the hydrogenation of acetophenone and benzonitrile in toluene when activated by KOtBu/KH. DFT studies were performed and a mechanism is proposed. The calculated rate limiting step for acetone hydrogenation was found to be heterolytic splitting of dihydrogen, which agrees well with experiment. The novel outer-sphere sequential hydrogenation of a CN triple bond and then a C=N double bond is proposed. A mechanism is proposed, which is supported by DFT studies, to explain the selectivity observed in the nucleophilic attack of amines or aziridines on palladium -prenyl phosphines complexes. Calculations on based on a palladium complex with two phosphorus donor ligands indicated that the observed selectivity would not be produced. Using two new model intermediates with either THF or aziridine substituted for a phosphine ligand trans to the unhindered side of the prenyl ligand did predict the experimentally observed selectivity.

<p>This thesis describes mechanistic studies, rational ligand design, and synthesis of asymmetric transition metal catalysts. The topics addressed concerned [Papers I-VII]:</p><p>[I] The asymmetric addition of diethyl zinc to <i>N</i>-(diphenylphosphinoyl)benzalimine catalyzed by bicyclic 2-azanorbornyl-3-methanols was studied. An efficient route to both diastereomers of new bicyclic 2-azanorbornyl-3-methanols with an additional chiral center was developed, in the best case 97% ee was obtained with these ligands. The experimental results were rationalized by a computational DFT-study.</p><p>[II] An aza-Diels-Alder reaction of cyclopentadiene with chiral heterocyclic imines derived from (<i>S</i>)-1-phenylethylamine and different heteroaromatic aldehydes was developed. The cycloaddition proved to be highly diastereoselective and offers a very rapid access to possible biologically active compounds and interesting precursors for chiral (<i>P,N</i>)-ligands. </p><p>[III] A convenient and high-yielding method for the preparation of (<i>R</i>)-tolterodine, utilizing a catalytic asymmetric Me-CBS reduction was developed. Highly enantio-enriched (<i>R</i>)-6-methyl-4-phenyl-3,4-dihydrochromen-2-one (94% ee) was recrystallized to yield practically enantiopure material (ee >99%) and converted to (<i>R</i>)-tolterodine in a four-step procedure. </p><p>[IV] The reaction mechanism of the iridium-phosphanooxazoline-catalyzed hydrogenation of unfunctionalized olefins has been studied by means of DFT-calculations (B3LYP) and kinetic experiments. The calculations suggest that the reaction involves an unexpected IrIII-IrV catalytic cycle facilitated by coordination of a second equivalent of dihydrogen. On the basis of the proposed catalytic cycle, calculations were performed on a full system with 88 atoms. These calculations were also used to explain the enantioselectivity displayed by the catalyst.</p><p>[V and VI] A new class of chiral (<i>P,N</i>)-ligands for the Ir-catalyzed asymmetric hydrogenation of aryl alkenes was developed. These new ligands proved to be highly efficient and tolerate a broad range of substrates. The enantiomeric excesses are, so far, the best reported and can be rationalized using the proposed selectivity model.</p><p>[VII] The complex formed between the quincorine-amine, containing both a primary and a quinuclidine amino function, and [Cp*RuCl]₄ catalyzes the hydrogenation of aromatic and aliphatic ketones in up to 90% ee approx. 24-times faster than previously reported Ru-diamine complexes. The reason for the lower but opposite stereoselectivity seen with the quincoridine-amine, as compared to the quincorine-amine, was rationalized by a kinetic and computational study of the mechanism. The theoretical calculations also revealed a significantly lower activation barrier for the alcohol mediated split of dihydrogen, as compared to the non-alchol mediated process. A finding of importance also for the diphosphine/diamine mediated enantioselective hydrogenation of ketones.</p>

This thesis describes mechanistic studies, rational ligand design, and synthesis of asymmetric transition metal catalysts. The topics addressed concerned [Papers I-VII]: [I] The asymmetric addition of diethyl zinc to N-(diphenylphosphinoyl)benzalimine catalyzed by bicyclic 2-azanorbornyl-3-methanols was studied. An efficient route to both diastereomers of new bicyclic 2-azanorbornyl-3-methanols with an additional chiral center was developed, in the best case 97% ee was obtained with these ligands. The experimental results were rationalized by a computational DFT-study. [II] An aza-Diels-Alder reaction of cyclopentadiene with chiral heterocyclic imines derived from (S)-1-phenylethylamine and different heteroaromatic aldehydes was developed. The cycloaddition proved to be highly diastereoselective and offers a very rapid access to possible biologically active compounds and interesting precursors for chiral (P,N)-ligands. [III] A convenient and high-yielding method for the preparation of (R)-tolterodine, utilizing a catalytic asymmetric Me-CBS reduction was developed. Highly enantio-enriched (R)-6-methyl-4-phenyl-3,4-dihydrochromen-2-one (94% ee) was recrystallized to yield practically enantiopure material (ee &gt;99%) and converted to (R)-tolterodine in a four-step procedure. [IV] The reaction mechanism of the iridium-phosphanooxazoline-catalyzed hydrogenation of unfunctionalized olefins has been studied by means of DFT-calculations (B3LYP) and kinetic experiments. The calculations suggest that the reaction involves an unexpected IrIII-IrV catalytic cycle facilitated by coordination of a second equivalent of dihydrogen. On the basis of the proposed catalytic cycle, calculations were performed on a full system with 88 atoms. These calculations were also used to explain the enantioselectivity displayed by the catalyst. [V and VI] A new class of chiral (P,N)-ligands for the Ir-catalyzed asymmetric hydrogenation of aryl alkenes was developed. These new ligands proved to be highly efficient and tolerate a broad range of substrates. The enantiomeric excesses are, so far, the best reported and can be rationalized using the proposed selectivity model. [VII] The complex formed between the quincorine-amine, containing both a primary and a quinuclidine amino function, and [Cp*RuCl]4 catalyzes the hydrogenation of aromatic and aliphatic ketones in up to 90% ee approx. 24-times faster than previously reported Ru-diamine complexes. The reason for the lower but opposite stereoselectivity seen with the quincoridine-amine, as compared to the quincorine-amine, was rationalized by a kinetic and computational study of the mechanism. The theoretical calculations also revealed a significantly lower activation barrier for the alcohol mediated split of dihydrogen, as compared to the non-alchol mediated process. A finding of importance also for the diphosphine/diamine mediated enantioselective hydrogenation of ketones.

Late transition metal complexes of silver(I), rhodium(I), ruthenium(II), palladium(II) and platinum(II) containing a nitrile-functionalized N-heterocyclic carbene ligand (C-CN) were prepared. The nitrile group on the C–CN ligand was shown to undergo hydrolysis under basic conditions, leading to a silver(I) carbene complex with a primary-amido functional group, and a trimetallic complex of palladium(II) with a partially hydrolyzed C–N–N–C donor ligand. The reduction of a nitrile-functionalized imidazolium salt in the presence of nickel(II) chloride under mild conditions yielded an axially chiral square-planar nickel(II) complex containing a unique primary-amino functionalized N-heterocyclic carbene ligand (C-NH2). A transmetalation reaction moved this chelating C–NH2 ligand from nickel(II) to ruthenium(II), osmium(II), and iridium(III), yielding important catalysts for the hydrogenation of polar double bonds. The ruthenium(II) complex, [Ru(p-cymene)(C–NH2)Cl]PF6 catalyzed the transfer and H2-hydrogenation of ketones. The bifunctional hydride complex, [Ru(p-cymene)(C–NH2)H]PF6, which contains a Ru–H/N–H couple showed no activity under catalytic conditions unless when activated by a base. The outer-sphere mechanism involving bifunctional catalysis of ketone reduction is disfavored according to experimental and theoretical studies and an inner-sphere mechanism is proposed involving the decoordination of the amine donor from the C–NH2 ligand. The ruthenium(II) complex [RuCp*(C–NH2)py]PF6 showed higher activity than the iridium(III) complex [IrCp*(C–NH2)Cl]PF6 in the hydrogenation of ketones. This ruthenium(II) complex also catalyzes the hydrogenation of an aromatic ester, a ketimine, and the hydrogenolysis of styrene oxide. We proposed an alcohol-assisted outer sphere bifunctional mechanism for both systems based on experimental findings and theoretical calculations. The cationic iridium(III) hydride complex, [IrCp*(C–NH2)H]PF6 , was prepared and this failed to react with a ketone in the absence of base. The crucial role of the alkoxide base was demonstrated in the activation of this hydride complex in catalysis. Calculations support the proposal that the base deprotonates the amine group of this hydride complex and triggers the migration of the hydride to the η5-Cp* ring producing a neutral iridium(I) amido complex. This system contains an active Ir–H/N–H couple required for the outer sphere hydrogenation of ketones in the bifunctional mechanism.

Late transition metal complexes of silver(I), rhodium(I), ruthenium(II), palladium(II) and platinum(II) containing a nitrile-functionalized N-heterocyclic carbene ligand (C-CN) were prepared. The nitrile group on the C–CN ligand was shown to undergo hydrolysis under basic conditions, leading to a silver(I) carbene complex with a primary-amido functional group, and a trimetallic complex of palladium(II) with a partially hydrolyzed C–N–N–C donor ligand. The reduction of a nitrile-functionalized imidazolium salt in the presence of nickel(II) chloride under mild conditions yielded an axially chiral square-planar nickel(II) complex containing a unique primary-amino functionalized N-heterocyclic carbene ligand (C-NH2). A transmetalation reaction moved this chelating C–NH2 ligand from nickel(II) to ruthenium(II), osmium(II), and iridium(III), yielding important catalysts for the hydrogenation of polar double bonds. The ruthenium(II) complex, [Ru(p-cymene)(C–NH2)Cl]PF6 catalyzed the transfer and H2-hydrogenation of ketones. The bifunctional hydride complex, [Ru(p-cymene)(C–NH2)H]PF6, which contains a Ru–H/N–H couple showed no activity under catalytic conditions unless when activated by a base. The outer-sphere mechanism involving bifunctional catalysis of ketone reduction is disfavored according to experimental and theoretical studies and an inner-sphere mechanism is proposed involving the decoordination of the amine donor from the C–NH2 ligand. The ruthenium(II) complex [RuCp*(C–NH2)py]PF6 showed higher activity than the iridium(III) complex [IrCp*(C–NH2)Cl]PF6 in the hydrogenation of ketones. This ruthenium(II) complex also catalyzes the hydrogenation of an aromatic ester, a ketimine, and the hydrogenolysis of styrene oxide. We proposed an alcohol-assisted outer sphere bifunctional mechanism for both systems based on experimental findings and theoretical calculations. The cationic iridium(III) hydride complex, [IrCp*(C–NH2)H]PF6 , was prepared and this failed to react with a ketone in the absence of base. The crucial role of the alkoxide base was demonstrated in the activation of this hydride complex in catalysis. Calculations support the proposal that the base deprotonates the amine group of this hydride complex and triggers the migration of the hydride to the η5-Cp* ring producing a neutral iridium(I) amido complex. This system contains an active Ir–H/N–H couple required for the outer sphere hydrogenation of ketones in the bifunctional mechanism.

Chapter 1: Metal carbenoids in organic synthesis The chapter describes the phenomena of metal carbenoid insertion reactions in two parts: Part A, and Part B. The study of N-tosylhydrazones as diazo precursor was commenced by Jose Barluenga in 2007,1 which demonstrated an in-situ generation of diazo species and trapping of that with low valent palladium catalyst (Scheme 1). Later, this palladium-carbenoid assumption was supported by few reports. Some of these discoveries were by D. F. Taber in 1986 followed by van Vranken in 1999 & 2001.2 These studies of palladium carbenes were supplemented by several groups in subsequent years. The consequent developments with N-tosylhydrazones as diazo source were very fruitful and produced exceptional chemical transformations in recent years. Though the precursor is also vastly customary for other metals such as Cu, Ni, Rh and Co, the primary focus has been given to Pd catalysis due to its wide utility and applicability. 1) Barluenga, J.; Moriel, P.; Valdes, C.; Aznar, F. Angew. Chem., Int. Ed. 2007, 46, 5587. 2) (a) Taber, D. F.; Amedio, J. C., Jr.; Sherrill, R. G. J. Org. Chem. 1986, 51, 3382. (b) Hoye, T. R.; Dinsmore, C. J.; Johnson, D. S.; Korkowski, P. F. J. Org. Chem. 1990, 55, 4518. (c) Greenman, K. L.; Carter, D. S.; Van Vranken, D. L Tetrahedron 2001, 57, 5219. 3) Palladium catalysed coupling of tosylhydrazones with aryl and heteroaryl halides in the absence of external ligands: synthesis of substituted olefins, Ojha, D. P.; Prabhu, K. R. J. Org. Chem., 2013, 78, 12136. Modes of reactivity of a metal-carbene Scheme 1 Cascade carbene migratory insertion process Part A: Ligand-free coupling of tosylhydrazones with aryl & heteroaryl halides In this part, Palladium catalysed cross-coupling reaction of hydrazones with aryl halides in absence of an external ligand is reported. The versatility of this coupling reaction has been demonstrated by showcasing the selectivity of coupling reaction in presence of hydroxyl and amine functional groups. This method allows synthesizing a variety of heterocyclic compounds, which are otherwise difficult to access from traditional methods. Application of the present methodology is validated in tandem reaction of ketones to the corresponding substituted olefins in a single pot experiment. Few examples are illustrated below in Scheme 2.3 Scheme 2: Scope of aryl halide coupling with tosylhydrazones Part B: Pd-catalysed Synthesis of Highly Branched Dienes The regioselective formation of highly branched dienes is a challenging task. Design and exploration of alternative working models to achieve such a regioselectivity to accomplish highly branched dienes is considered to be a historical advancement of Heck reaction to construct branched dienes. On the basis of the utility of carbene transfer reactions, in the reaction of hydrazones with Pd(II) under oxidative conditions, we envisioned obtaining a Pd-bis-carbene complex with α-hydrogens, which can lead to branched dienes. Herein, we report a novel Pd catalyzed selective coupling reaction of hydrazones in presence of tert-BuOLi and benzoquinone oxidant to form corresponding branched dienes (Scheme 3).4 The utility of the Pd catalyst for cross-coupling reactions for synthesizing branched conjugated dienes are rare. The reaction is very versatile and compatible with a variety of functional groups and is useful in synthesizing heterocyclic molecules. We anticipate that this Pd-catalyzed cross-coupling reaction will open new avenues for synthesizing useful compounds. 4) Pd-catalyzed cross-coupling reactions of hydrazones: regioselective synthesis of highly branched dienes, Ojha, D. P.; Prabhu, K. R. J. Org. Chem., 2012, 77, 11027. 5) Furrow, M. E.; Myers, A. G. J. Am. Chem. Soc. 2004, 126, 5436. 6) Taber, D. F.; Guo, P.; Guo, N. J. Am. Chem. Soc. 2010, 132, 11179. Scheme 3: diene synthesis via bis-carbene insertion process Chapter 2: Tosylhydrazones: Role in modern day organic synthesis In recent days, hydrazone based reactions are focused on the donor-acceptor ability of the hydrazones or the in-situ generated diazo species (Scheme 4). This commenced with the Myers’s report in 2004,5 which simplifies the Barton vinyl halide preparation with a remarkable revision on synthesis of alkyl-silyl-hydrazones and its applications. Improved methods of using tosylhydrazones were demonstrated by Aggarwal in successive years. Cycloadditions were implemented by Douglass F. Taber. 6 This study was enriched in a quite fascinating way by several groups such as Jose Barluenga, with many reductive coupling reactions and 1, 3-dipolar reactions. Thomson, in a very interesting report shows the traceless petasis reaction with hydrazones and also worked in many other prospects such as three component reactions and the acid catalysed [3+3] sigmatropic reactions of hydrazones. 7 Wang has also impressed with very attractive transformations in the past decade. 8 7) Thomson, R. J. et al. Nat. Chem. 2009, 1, 494. 8) Xiao, Q.; Zhang, Y.; Wang, J. Acc. Chem. Res. 2012, 46, 236. 9) Regioselective Synthesis of vinyl halides, vinyl sulfones, and alkynes: A tandem intermolecular nucleophilic and electrophilic vinylation of tosylhydrazones, Ojha, D. P.; Prabhu, K. R. Org. Lett. 2015, 17, 18. Scheme 4: Trapping diazo species in intermolecular fashion Part A: Synthesis of vinyl halides Trapping diazo species in an intermolecular fashion by attack of two independent ions (a cation followed by an anion) in tandem at the carbene center is unprecedented. As part of our efforts on the utility of tosylhydrazones, herein we report a novel approach of using ambiphilic diazo species to perform a tandem attack of a nucleophile followed by an electrophile in an intermolecular fashion for synthesizing various types of vinyl halides. A few representative examples are shown in Scheme 5.9 Scheme5: Synthesis if vinyl halides Part B: Synthesis of vinyl sulfones Vinyl sulfones are potential synthetic targets due to their presence in biologically and pharmaceutically important molecules ranging from small natural metabolites to proteins, and have found widespread applications in biological research as covalent protease inhibitors. Vinyl sulfones represent one of the important sulfur containing functional groups in organic chemistry, which are generally synthesized through elimination reactions, oxidation of vinyl sulfides or witting reactions using multistep sequence. Following this technique, we were able to synthesize a variety of vinyl sulfones with rich mechanistic features in a single step. A few such examples are documented in Scheme 6.9 Scheme 6: synthesis of vinyl sulfones Part C: Synthesis of alkynes The functional group conversion to achieve alkyne frameworks are generally a difficult transformation. There are very few limited and tedious processes are available in literature, mainly containing multi-step procedures. Additionally these reactions are require harsh conditions. Considering all these factors, there is a need for developing methods to synthesize alkynes from common functional groups under mild reactions conditions. In a similar way, to introduce different halogens at the same carbon, we expected the eliminations of the leaving groups in tandem formed alkynes. After extensive screening studies, it was pleasing to find that the reaction of tosylhydrazones with NCS−BTEAC, NBS−TBAB, or NIS−TBAI combination in presence of K2CO3 in dioxane as solvent at 110 °C can furnish corresponding acetylene derivatives in good yields. Few examples are shown in Scheme 7.9 Scheme 7: Trapping diazo species in intermolecular fashion Chapter 3: Pd catalysed hydroboration This chapter shows a hydroboration study of terminal alkynes in a highly regioselective manner (Scheme 8). Organoboron derivatives have become essential intermediates in organic and medicinal chemistry. Pioneering contributions are made by Brown and Akira Suzuki, who both instigated the development of new synthetic tools for the introduction of boron atoms onto organic molecules. 10 10) (a) Barbeyron, R.; Benedetti, E.; Cossy, J.; Vasseur, J.-J.; Arseniyadis, S.; Smietana, M. Tetrahedron 2014, 70, 8431. (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. 11) Pd-Catalysed regioselective borylation of alkynes: A ligand controlled synthesis of α- and β vinyl boronates (manuscript submitted). Scheme 8: possibility of site selectivity in hydroboration Part A: Pd-catalysed regioselective borylation of alkynes: A ligand controlled synthesis of α and β – vinyl boronates The metal catalyzed borylations of alkynes proceeds in a two-step process. Initially M-Bpin species undergo an addition onto the alkynes to generate organometallic species followed by quenching of the organometallic species with electrophiles. The addition M-Bpin species is regioselective governed by the steric and electronics factors of both metal complex as well as alkyne substituents. In this direction, a palladium catalysed α-selective borylation was achieved for terminal alkynes. A broad range of substrates were successfully borylated under optimized reaction conditions with very high selectivity. Interestingly, the selectivity was reversed to terminal site by using a NHC ligand. A few examples are shown in Scheme 9.11 Scheme 9: α & β-vinyl boronates Chapter 4: Pd/borane unit: Behavior towards isomerization vs reduction of alkenes This study presents a unique behaviour of palladium-boronate unit responsible for olefin chain walking and olefin reduction reactions (Scheme 10). The catalytic system stands efficient against both functionalized and unfunctionalized olefin isomerization as well as reductions. This study has been presented in two parts. Scheme 10: isomerization vs reduction Part A: Pd/ boronates or borane unit as efficient catalytic systems for olefin chain walk This study presents the behaviour of palladium-boronate unit responsible for olefin chain walking. The catalytic system is efficient for both functionalized and unfunctionalized olefin isomerizations (Scheme 11). Cycloisomerization of transient conjugated alkenes to synthesize heterocycles are prominent applications of this technique. The system describes a concept of olefin activation by coordination with Pd-borane complex, this complex assists in a facile [1,3]-hydride shift. This technique allows us to facilitate an isomerization in functionalized as well as unfunctionalized olefinic systems. Considering the substrates scope, the catalytic cycle tolerates various sensitive functional groups and shows good selectivity. In the following Scheme 11 few examples are depicted.12 12) Palladium/boron catalytic unit for olefin chain-walk (manuscript under preparation). Scheme 11: chain-walking of olefins. Part B: Palladium catalysed boronate promoted alkene reduction in water In this work, water has been employed as a source of hydrogen. The reduction of alkenes was achieved using Pd catalyst in presence of bis(pinacolato)diboron and H2O. In this aspect, the utility of water as hydrogen equivalent is the pertinent as well as beneficial with many advantages. Few representative examples are shown in Scheme 12.13 13) Pd-Catalysed homogeneous hydrogenation of olefins by using water as hydrogen source (manuscript under preparation). Scheme 12: synthesis of alkenes reduced products.