Linear homobimetallic palladium complexes

The oxidative addition of C6H4-1,4-I2 (1) to Pd(PPh3)4 (2) gives mononuclear trans-(Ph3P)2Pd(C6H4-4-I)(I) (3), which can be converted to trans-(Ph3P)2Pd(C6H4-4-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-(Ph3P)2Pd(C6H4-4-I)(L)]+ (7, L = C4H4N2; 9a, L = C5H4N-4-CN; 9b, L = NC-4-C5H4N) and [trans-(C6H4-4-I)(Ph3P)2Pd ← N∩N → Pd(PPh3)2(C6H4-4-I)]2+ (14a, N∩N = C6H4-1,4-(CN)2; 14b, N∩N = (C6H4-4-CN)2; 14c, N∩N = 4,4′-bipyridine (=bipy)). Complexes 7, 9 and 14 rearrange in solution to give [trans-(Ph3P)2Pd(C6H4-4-PPh3)(L)]2+ (10, L = C4H4N2; 12a, L = C5H4N-4-CN; 12b, L = NC-4-C5H4N) and [trans-(C6H4-4-PPh3)(Ph3P)2Pd ← N∩N → Pd(PPh3)2(C6H4-4-PPh3)]4+ (15a, N∩N = C6H4-1,4-(CN)2; 15b, N∩N = (C6H4-4-CN)2) along with {[(Ph3P)2(Ph3P-4-C6H4)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 PPh3 ligands. In 3 the iodide and the 4-iodo-benzene are linear oriented laying with the palladium atom on a crystallographic C2 axes. In 9a this symmetry is broken by steric interactions of the PPh3 ligands with the 4-cyanopyridine and 4-iodobenzene groups. Compound 11 contains two μ-bridging iodides with different Pd–I separations showing that the C6H4PPh3+ ligand induces a stronger trans-influence than PPh3. In 15b, the Ph3PC6H4Pd ← NCC6H4C6H4CN → PdC6H4PPh3 building block is rigid-rod structured with the C6H4 units perpendicular oriented to the Pd coordination plane, while the biphenylene connecting moiety is in-plane bound.

Graphical abstractThe synthesis and reaction chemistry of trans-(Ph3P)2Pd(C6H4-4-I)(X) (X = I, OTf) is discussed. Treatment of trans-(Ph3P)2Pd(C6H4-4-I)(OTf) with bidentate Lewis-bases N∩N (N∩N = pz, bipy, (C6H4-4-CN)2, C5H4N-4-CN, C6H4-1,4-(CN)2) produces, depending on N∩N, mono- or homobimetallic species of structural type [trans-(C6H4-4-X)(Ph3P)2Pd(N∩N)]n+ (X = I, n = 1; X = PPh3, n = 2), [trans-(C6H4-4-X)(Ph3P)2Pd ← N∩N → Pd(PPh3)2(C6H4-4-X)]n+ (X = I, n = 2; X = PPh3, n = 4) and {[(Ph3P)2(Ph3P-4-C6H4)Pd(μ-I)]2}2+. The solid state structures of five species is reported.Figure optionsDownload full-size imageDownload as PowerPoint slide