Allenyl-propargyl tautomerism at palladium(IV) and platinum(IV) centres

The propargylic bromides MeC=CCH2Br and HC=CCH2Br undergo oxidative addition reactions with [MMe2{(pz)(3)BH}](-) {M = Pd, Pt; [(pz)(3)BH](-) = tris(pyrazol-1-yl)borate}, [Pd(CH2CH2CH2CH2){(pz)(3)BH}](-) and MMe2(bpy) (M = Pd, Pt; bpy = 2,2'-bipyridine) to form the octahedral metal(IV) complexes MMe2(CH2C=CMe){(pz)(3)BH} [M = Pd (1), Pt (3)], Pd(CH2CH(2)CH(2)CH(2))(CH2C=CMe){(pz)(3)BH} (2), Pd(CH2CH2CH2CH2)(CH=C=CH2) {(pz)(3)BH} (5), PdMe2(CH=C=CH2) {(pz)(3)BH} (4), a mixture of tautomers PtMe2(CH2C=CH){(pz)(3)BH} (6a) and PtMe2(CH=C=CH2){(pz)(3)BH} (6b), MBrMe2 (CH2C=CMe)(bpy) [M = Pd (7), Pt (8)], a mixture of structural isomers PdBrMe2(CH2C=CH)(bpy) with the propargyl group trans to bromine (9a) and bpy (9b), and a mixture of tautomers and structural isomers for PtBrMe2(CH2C=CH)(bpy) (10a, 10b) and PtBrMe2(CH=C=CH2)(bpy) (10c, 10d). The preference for adoption of the propargyl or allenyl form is dependent upon metal, ancillary ligands, and substitution in the propargyl/allenyl fragment M-C3H3 and M-C3H2Me: for M-C3H2Me propargyl is favoured and for M-C3H3 allenyl is favoured for the Pd(IV)/[(pz)(3)BH](-) substrates but propargyl is favoured for the Pd(IV)/bpy substrate. (C) 1999 Elsevier Science S.A. All rights reserved.