Tetranuclear amido complexes of copper(I): a synthetic and structural study
Abstract
Reaction of copper(I) halides with lithium amides leads to the formation of thermally stable tetrameric amido derivatives of copper(I), [{Cu(NRR′)}4][NRR′= NMe2, (1); [graphic omitted]H2, (2); MeNCH2CH2NMe2, (3); N (CH2CH2NEt2)2, (4)]. Compounds (1)–(4) are tetrameric both in the solid state (X-ray analysis) and in solution (cryoscopy in benzene). Copper(I) remains consistently two-co-ordinate without bonding the free amino groups in complexes (3) and (4). Copper(I) amido complexes did not react with unidentate ligands like PPh3 and NEt3 but complex (2) undergoes a facile transformation with bis(diphenylphosphino)methane (dppm) and 1,2-bis(diphenylphosphino)ethane (dppe). The amido group abstracts a proton from dppm forming the known trimeric compound [Cu3(PPh2CHPPh2)3](5), while it promotes the cleavage of a P–C bond in dppe, forming [Cu2(µ-PPh2)2(dppe)2](6). The structures of complexes (1)–(3) have been determined by X-ray analysis. They each have an eight-membered ring, Cu4N4, which is nearly planar for complexes (1) and (2), but significantly distorted from planarity for (3). The average Cu–N bond distances are very similar: 1.890(5) in (1), 1.885(4) in (2), 1.913(4)Å in (3); the Cu ⋯ Cu separations are 2.702(2) in (1), 2.717(2) in (2), and 2.618(2)Å in (3). Copper(I) has a nearly linear two-co-ordinate geometry in all the complexes, the N–Cu–N angle being 178.5(2) in (1), 177.1(2) in (2), and 169.4(2)° in (3).