SYNTHESIS AND STRUCTURE OF PLATINUM-TUNGSTEN AND PLATINUM-MOLYBDENUM HETERODINUCLEAR COMPLEXES WITH ALKYL AND ARYL LIGANDS - MECHANISTIC STUDY OF THE MIGRATION OF ALKYL AND ARYL GROUPS FROM PLATINUM TO TUNGSTEN AND MOLYBDENUM

A series of heterodinuclear platinum - tungsten and - molybdenum compl exes (cod)RPt-M(CP)(CO)3 has been prepared by the metathetical reactio ns: M = W, Cp = Cp, R = Me (1a), Et (1b), Ph (1c), 2-MeC6H4 (1d), 4-Me C6H4 (1e), 2,6-(Me)2C6H3 (1f), 4-MeOC6H4 (1g), C6F5 (1h), 4-FC6H4 (1i) , 4-ClC6H4 (1j); M = W, CP = C5H4Me, R = Me (2a), Ph (2b), M = W, Cp = C5H4COOMe, R = Me (3a), Ph (3b); M = Mo, CP = Cp, R = Me (4a), Ph (4b ), 2-MeC6H4 (4c). (cod)PhPt-MoCp(CO)3 (4b) crystallizes in the monocli nic system in space group P2(1)/n with a = 14.291(5) angstrom, b = 12. 738(3) angstrom, c = 11.988(4) angstrom, beta = 112.01(3)-degrees, Z = 4, R = 0.057 (R(w) = 0.078), based on 3719 reflections with \F(o)\ > 3sigma(\F(o)\. 4b is isostructural to the Pt-W analogue 1c determined previously and the geometry at Pt is square planar, where the Pt-Mo bo nd distance is 2.832(1) angstrom. The alkyl and aryl ligands on Pt mig rate to the other metal in thermolysis in C6D6 at 70-degrees-C. The mi gration is accelerated by CO as well as by PPh3 or P(OPh)3. In contras t, the reaction of 1a with PMe3 does not result in the methyl migratio n but affords [PtMe(PMe3)3]+ [WCp(CO)3]- (5). Moreover, the migration is accelerated by acrylonitrile and the rate is first order in the con centration of acrylonitrile, but further addition of COD retards the r ate of migration. From kinetic investigation, the mechanism of the met hyl migration for 1a is proposed. In the mechanism, acrylonitrile coor dinates to 1a to form a five-coordinated intermediate (6), and 6 disso ciates COD to form a three-coordinated intermediate (7). MeWCp(CO)3 (8 ) is produced from 1a, 6, and 7.