kJ mol-1, and similar isomerisation of cis-[PtC12pyz] (py = pyridine) has A H = -20 kJ mol-l. Clearly no solvation effects can favour the trans-isomers, but changes in the crystal lattice energies could be considerable with these small, polar ligands. A solid-state ti-ans-cis-isomerisation of [PtCl~(pms)2] (pms = l

The term "insertion" is widely used in organometallic chemistry to describe a large class of reactions, yet it is a term that is frequently misleading. It is used to describe the process whereby an unsaturated moiety, which may or may not be coordinated to the metal initially, becomes bonded to the metal and to a saturated ligand (which was initially attached to the metal

In a similar manner, the cyclopentadienyl complex [Au(C,H,)( PPh,) ] can conveniently be made from [AuCI( PPh,) 1, Na(OEt), and C, H, . The phosphine of [Au(C-CPh)L] rapidly exchanges in solution with free phosphines. The compounds [Au( C=CPh)( PPh,) ] and [AuCI{ P( C,H,Me-p),}] readily equilibrate with [AuCI( PPh,)] and [Au(C=CPh){P(C,H,Me-p),}], a reaction which could also involve exchange of phosphines, but the exchange of CI for C&Ph is another possible pathway. Phenylethynyl groups from [Au(CzCPh)( PPh,)] exchange with both chlorides of HgCI,, cis-[PtCI,( PMePh,),], and cis-[ PtCI,(CO)( PMePh,) 3. With the latter complex the exchange is non -stereospecific, unlike related reactions with organomercurials.

t31P) and n.m.r. measurements on the triphosphazanes (Ph,P*NR),PPh show that J(PNP) is +280 Hz when R = Me and 25.1 Hz when R = Et. A similar marked dependence on the R groups has been found for the diphosphinoamines, Ph,P*NR*PPhCI (R = Me, Et, Pr", Pr', and But) (+334 to -35 Hz), and this may be related to the conformations about the P-N bonds, which are influenced by the stereochemical bulk of R. 1H-(31P) INDOR experiments on the symmetrical diphosphinoamines, Ph,P*NR*PPh, (R = Me, Et, and Pr'), indicate that J ( P N P ) is much greater when R = Me than when R = Et or Pr'.

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