The reactions of acrylic and vinylacetic acids with Ph2PCl and Et3N give Ph2PO2CCH=CH2 (AAA) and Ph2PO2CCH2CH=CH2 (VAA) respectively. Both are found to undergo a facile rearrangment to give Ph2PP(O)Ph2 and AAA is also found to react with PPh3 to give Ph3P+-CH2CH2CO2-. Their reaction (1 mole ligand to 1 mole Rh) with [(RhCl(1,5 COD))2], gives complexes of the form [(RhCl(L)2], where L is AAA or VAA, in which the mixed anhydride ligands are bound via the phosphorus atom and the double bond. With AAA in a 1:2 mole reaction with [(RhCl(1,5 COD))2] or a 1:1 mole reaction with [(RhCl(C2H4)2)2l, the major products are [(RhCl(AAA))2 (Ph2POPPh2)] and [RhCl(AAA)2], in which the mixed anhydride is bound as described above and the Ph2POPPh2 is a bridging ligand. Reaction (1:1) of AAA with [RhCl(PPh3)3] led to the formation of [RhCl(AAA)(PPh3)]; anhydride coordination is as above and the phosphorus atoms are mutually trans. This complex is, however, found to revert back to [RhCl(PPh3)3] on standing. The (1:1) reaction with VAA produces [RhC1(PPh3) (Ph2PO2CCH = CHMe)] (Ph2PO2CCH=CHMe = CAA), an example of a metal promoted double bond migration. Subsequent study shows that at ambient pressure and temperature this complex (with 3 butenoic, oleic and hexa-4-enoic acids) is involved in stoichiometric and not catalytic reactions. [RhCl(CAA)(PPh3)] exhibits fluxionality at room temperature, 31p and 1H n.m.r, studies on this complex (223-263K) and on [Rh(CAA)(O2CCH=CHMe)(PPh3)] (298K) has determined the fluxionality to be a fast exchange between the cis and trans forms and led to the calculation of the thermodynamic parameters for this process . The 1:2 mole reaction of [RhCl(PPh3)3] and AAA gives lRhCl(PPh3)(Ph2POPPh2)], which contains a chelate tetraphenyl diphosphoxane ligand (tpdp) formed via a metal promoted rearrangement of the AAA ligand. Subsequent reaction of this complex with TIPF6 results in [Rh(PPh3)2(tpdp)][PF6]. However if the [RhCl(PPh3)(tpdp)] complex is not isolated, then the major product is [Rh(PPh3)3(Ph3PCH2CH2CO2)][PF6]. Further tpdp complexes have been formed by refluxing Ph2PP(O)Ph2 with [RhCl(PPh3)3], [RuCl2(PPh3)4] and [OsCl2(PPh3)4] in THF. However the reaction of [RhCl(PPh3)3] with excess Ph2PP(O)Ph2 gives several products, one of which, namely [RhCl2((PPh2O)2)H(PPh2O)][HNEt3], has been crystallographically characterised. The reaction (1:1) of [RuCl2(PPh3)4] with Ph2PO2CCHCMe2 (DAA) produces [RuCl2(PPh3)2(DAA)], in which the mixed anhydride is bound via the phosphorus atom and the oxygen atom of the carbonyl group. The 1:1 mole reactions of CAA and AAA give similar complexes as minor products whilst the structure of the major product is, however, not known at this point in time. The 1:2 mole reaction was found to produce [RuCl2(tpdp)(AAA)(PPh3)] in which the mixed anhydride is bound via the phosphorus atom alone.