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

The propargylic bromides MeCCCH 2Br and HCCCH 2Br undergo oxidative addition reactions with [MMe 2{(pz) 3BH}] - {M=Pd, Pt; [(pz) 3BH] -=tris(pyrazol-1-yl)borate}, [Pd(CH 2CH 2CH 2CH 2){(pz) 3BH}] - and MMe 2(bpy) (M=Pd, Pt; bpy=2,2′-bipyridine) to form the octahedral metal(IV) complexes MMe 2(CH 2CCMe){(pz) 3BH} [M=Pd (1), Pt (3)], Pd(CH 2CH 2CH 2CH 2)(CH 2CCMe){(pz) 3BH} (2), Pd(CH 2CH 2CH 2CH 2)(CH=C=CH 2){(pz) 3BH} (5), PdMe 2(CH=C=CH 2){(pz) 3BH} (4), a mixture of tautomers PtMe 2(CH 2CCH){(pz) 3BH} (6a) and PtMe 2(CH=C=CH 2){(pz) 3BH} (6b), MBrMe 2(CH 2CCMe)(bpy) [M=Pd (7), Pt (8)], a mixture of structural isomers PdBrMe 2(CH 2CCH)(bpy) with the propargyl group trans to bromine (9a) and bpy (9b), and a mixture of tautomers and structural isomers for PtBrMe 2(CH 2CCH)(bpy) (10a, 10b) and PtBrMe 2(CH=C=CH 2)(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-C 3H 3 and M-C 3H 2Me: for M-C 3H 2Me propargyl is favoured and for M-C 3H 3 allenyl is favoured for the Pd(IV)/[(pz) 3BH] - substrates but propargyl is favoured for the Pd(IV)/bpy substrate.