Linear homobimetallic palladium complexes

Abstract

The oxidative addition of C 6H 4-1,4-I 2 ( 1) to Pd(PPh 3) 4 ( 2) gives mononuclear trans-(Ph 3P) 2Pd(C 6H 4-4-I)(I) ( 3), which can be converted to trans-(Ph 3P) 2Pd(C 6H 4-4-I)(OTf) ( 5) by its reaction with [AgOTf] ( 4). Complex 5 can be used in the high-yield preparation of a series of unique cationic mono- and dinuclear palladium complexes of structural type [ trans-(Ph 3P) 2Pd(C 6H 4-4-I)(L)] + ( 7, L = C 4H 4N 2; 9a, L = C 5H 4N-4-C N; 9b, L = N C-4-C 5H 4N) and [ trans-(C 6H 4-4-I)(Ph 3P) 2Pd ← N ∩N → Pd(PPh 3) 2(C 6H 4-4-I)] 2+ ( 14a, N ∩N = C 6H 4-1,4-(C N) 2; 14b, N ∩N = (C 6H 4-4-C N) 2; 14c, N ∩N = 4,4′-bipyridine (=bipy)). Complexes 7, 9 and 14 rearrange in solution to give [ trans-(Ph 3P) 2Pd(C 6H 4-4-PPh 3)(L)] 2+ ( 10, L = C 4H 4N 2; 12a, L = C 5H 4N-4-C N; 12b, L = N C-4-C 5H 4N) and [ trans-(C 6H 4-4-PPh 3)(Ph 3P) 2Pd ← N ∩N → Pd(PPh 3) 2(C 6H 4-4-PPh 3)] 4+ ( 15a, N ∩N = C 6H 4-1,4-(C N) 2; 15b, N ∩N = (C 6H 4-4-C N) 2) along with {[(Ph 3P) 2(Ph 3P-4-C 6H 4)Pd(μ-I)] 2} 2+ ( 11). The solid state structures of 3, 9a, 10, 11 and 15b are reported. Most characteristic for all complexes is the square-planar coordination geometry of palladium with trans-positioned PPh 3 ligands. In 3 the iodide and the 4-iodo-benzene are linear oriented laying with the palladium atom on a crystallographic C 2 axes. In 9a this symmetry is broken by steric interactions of the PPh 3 ligands with the 4-cyanopyridine and 4-iodobenzene groups. Compound 11 contains two μ-bridging iodides with different Pd–I separations showing that the C 6 H 4 PPh 3 + ligand induces a stronger trans-influence than PPh 3. In 15b, the Ph 3PC 6H 4 Pd ← N C C 6H 4 C 6H 4 C N → Pd C 6H 4PPh 3 building block is rigid-rod structured with the C 6H 4 units perpendicular oriented to the Pd coordination plane, while the biphenylene connecting moiety is in-plane bound.