Studies of transition metal phosphine complexes relevant to catalysis

Abstract

Methoxycarbonyl compounds of the type [Pd(X)(CO(_2)Me)(L(_2))] (1) and [Pd(X)(CO(_2)Me)(L)(_2)] (2) were used as models in the work related to hydroesterification using methyl formate instead of CO and MeOH. The behaviour of the complexes (1) and (2) in solution was examined, as was their behaviour in the presence of alkenes and nucleophiles. Many of these derivatives were too unstable to isolate, forming the corresponding dichloride complexes [Pd(X)(_2)(L(_2))] (3) and [Pd(X)(_2)(L)(_2)] (4). Several crystal structures of such complexes were obtained. The cationic complex [Pd(CO(_2)Me)(MeCN)(PPh(_3))(_2)](BF(_4)) (5) was synthesised from (2) by removal of the chloride ligand with silver tetrafluoroborate. This is the first isolated cationic methoxycarbonyl complex of palladium. A crystal structure of (5) was obtained. Some of the factors which affected the stability of methoxycarbonyl complexes were examined. Some of these systems were used as precursors for catalytic studies of hydroesterification. The second part of the work involved the chemistry of an unusual phosphine ligand and sohie of its analogues. The bidentate ligand dppn (6) has been reacted with some first row transition metal halides to give novel complexes such as [NiCl(_2)(dppn)] (7) and [CoCl(_2)(dppno)] (8). The ligand (6) also reacted with [Pd(MeCN)(_4)](BF(_4))(_2) (9) to give [Pd(MeCN)(_2)(dppn)](BF(_4))(_2) (10). Upon addition of dppe to (10), the acetonitrile and dppn ligands were entirely replaced by dppe to give the complex [Pd(dppe)(_2)](BF(_4))(_2) (11). When dppe was added to the nickel complex (7), the dppe displaced the chelating dppn ligand to give [NiCl(_2)(dppe)] (12) and free dppn. The cyclohexyl analogue of dppn, called dcpn (13) was synthesised. The complexes [PdCl(_2)dcpn)] (14) and [Pd(MeCN)(_2)(dcpn)](BF(_4))(_2) were made using the ligand (13). The phosphine oxides of (6) and (13) were made by exposure to air in solution. These compounds are called dpno (15) and dcno (16) respectively. Preliminary catalytic work using the ligand (6) was carried out.