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

Abstract

The propargylic bromides MeCCCH2Br and HCCCH2Br undergo oxidative addition reactions with [MMe2{(pz)3BH}]- {M = Pd, Pt; [(pz)3BH]- = tris(pyrazol-1-yl)borate}, [Pd(CH2CH2CH2CH2){(pz)3BH}]- and MMe2(bpy) (M = Pd, Pt; bpy = 2,2'-bipyridine) to form the octahedral metal(IV) complexes MMe2(CH2CCMe){(pz)3BH} [M = Pd (1), Pt (3)], Pd(CH2CH2CH2CH2)(CH2CCMe){(pz)3BH} (2), Pd(CH2CH2CH2CH2)(CH=C=CH2){(pz)3BH} (5), PdMe2(CH=C=CH2){(pz)3BH} (4), a mixture of tautomers PtMe2(CH2CCH){(pz)3BH} (6a) and PtMe2(CH=C=CH2){(pz)3BH} (6b), MBrMe2(CH2CCMe)(bpy) [M = Pd (7), Pt (8)], a mixture of structural isomers PdBrMe2(CH2CCH)(bpy) with the propargyl group trans to bromine (9a) and bpy (9b), and a mixture of tautomers and structural isomers for PtBrMe2(CH2CCH)(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)3BH]- substrates but propargyl is favoured for the Pd(IV):bpy substrate.