The Influence of Steric Pressure on the Structure of Homodimetallic Rhodium(I) and Iridium(I) Complexes Containing a Bis(bidentate) Phosphane Ligand

Abstract

AbstractFifteen novel homodimetallic RhI and IrI complexes containing the bis(bidentate) phosphane ligand cis,trans,cis‐1,2,3,4‐tetrakis(diphenylphosphanyl)cyclobutane (dppcb) were prepared and characterized by NMR spectroscopy (1H, 13C{1H}, 31P{1H}), mass spectrometry, IR spectroscopy, elemental analyses and melting points. Furthermore, the solid‐state structures of seven of these new compounds were fully determined by single‐crystal X‐ray diffraction analyses to study the influence of steric pressure. The precursor complex [Rh2(η4‐cod)2(dppcb)]X2 (1), X– = BF4–, PF6–, SbF6–, completely characterized by its X‐ray structure, smoothly reacts with mono‐ or bidentate ligands containing phosphorus or nitrogen donor atoms. Thus, monophosphanes and monophosphites produce compounds of the structure type [Rh2L4(dppcb)](SbF6)2 [L = PMe2Ph, 2; PMePh2, 3; P(OMe)3, 5; P(OPh)3, 6]. The X‐ray structures of 3 and 6 show that PMePh2 and P(OPh)3 are capable of compensating steric interactions. The treatment of 1 with diphosphanes leads to the structure type [Rh2L2(dppcb)](SbF6)2 [L = bis(diphosphanyl)methane, dppm, 7; bis(diphenylphosphanyl)amine, dppam, 8; 1,2‐bis(diphenylphosphanyl)ethane, dppe, 9; cis‐1,2‐bis(diphenylphosphanyl)ethene, cis‐dppen, 10]. The X‐ray structures of 8, 9 and 10 clearly indicate the onset of steric pressure as a consequence of mechanical coupling, which results in two different coordination moieties for homodimetallic species 9 and 10. Under steric pressure, the quadrant effects of dppcb and dppe become comparable to RhI complexes. The use of mono‐ or bidentate ligands containing nitrogen donor atoms leads to the compounds [Rh2(pyridine)4(dppcb)](SbF6)2 (11), [Rh2(2,2′‐bipyridine)2(dppcb)](SbF6)2 (12) and [Rh2(1,10‐phenanthroline)2(dppcb)](SbF6)2 (13). The crystal structures of 1 and the novel complex [Ir2(η4‐cod)2(dppcb)]X2 (14), X– = BF4–, SbF6–, are isomorphous. However, it was only possible to produce restricted examples of derivatives of 14 owing to the reluctance of 14 to release cod. Thus, monophosphanes lead to the five‐coordinate species [Ir2(η4‐cod)2(PMe2Ph)2(dppcb)](BF4)2 (15), whereas the four‐coordinate compound [Ir2(PMePh2)4(dppcb)](BF4)2 (16) is formed by using the sterically more demanding ligand PMePh2 instead of PMe2Ph. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)