Trimeric Iridium(I) and Iridium(III) Complexes with the Tripodal Phosphane cis, cis‐1,3,5‐Tris[(diphenylphosphanyl)methyl]cyclohexane (tdppmcy) as Bridging Ligand

Abstract

The excellent ligating properties of tertiary phosphanes have made them important constituents of compounds used for catalysis"], study of structure-bonding relationships, and spectroscopic studied2]. In this context, polyphosphanes have been developed to improve the stability and to control the stereochemistry and reactivity of transition metal complexe~ [~~~]. Polyphosphanes can act as both chelating and bridging ligands, depending on the design of the backbone. In general, the thermodynamic advantage of the chelate effect favors the formation of five-and six-membered rings as compared to the bridging mode. If the bite angle becomes small the bridging mode is observed as well as four-membered rings. If the ring size becomes larger (>7) the bridging mode is preferredI5I. Although the C, symmetry of the ligands should generate pyramidal metal complexes, the use of the cyclohexane ring as backbone in tripodal phosphane ligands results in different coordination behaviorr6-*]. We report here on the coordination chemistry of the tripodal phosphane ligand cis,cis-l,3,5-tris[(diphenylphosphanyl)methyl]cyclohexane (tdppmcy)[61 (1) which forms trinuclear iridium complexes. Trimeric Iridium Complex 2Treatment of Ir(PPh3),(CO)C1 with the potentially tripodal phosphane ligand cis, cis-1,3,5-tris[(diphenylphosphanyl)methyl]cyclohexane (tdppmcy) (1) in a stoichiometric ratio of 3:2 in hot toluene gives the trinuclear tris(carbony1-chloroiridium) complex 2 in high yield (Scheme 1). The composition of 2 has been established by elemental analysis, mass spectrometry, and molecular mass studies. The molecule consists of two tdppmcy (1) ligands held together by three bridging iridium atoms. Each of the three metal centers is trans-coordinated by two diphenylphosphanyl groups of two different tdppmcy ligands, one chlorine and one carbony1 ligand in a square-planar way. The stereochemistry around the coordination centers is thus the same as in Vaska's complex Ir(PPh3)2(CO)Cl[91. This is nicely demonstrated by their IR spectra. The v(C0) absorption at 1957 cm-' of 2 differs from Vaska's complex by only 7 wave numbers. It is observed at a higher energy (>60 wave numbers) than would be expected if all three phosphane groups of one tdppmcy ligand are connected to the same metal center[*, lol.

Synthesis and Reactivity of Iridium(I) Fluorido Complexes: Oxidative Addition of SF4 at trans‐[Ir(F)(CO)(PEt3)2]

“…[17] Compound 6Ј reveals the expected doublet of triplet pattern in the 13 C{ 1 H} NMR spectrum in the range of iridium(I) bound carbonyl ligands at δ = 174.1 ppm. [17,18] A very intense absorption band at 1925 cm -1 for the CO stretch mode can be detected in the IR spectrum of 6 (1878 cm -1 for 6Ј) which is well comparable to the known iridium based Vaska type complexes. [12a,19] Compound 6 shows a significantly lower wavenumber than the compounds bearing heavier halogenido ligands.…”

“…An additional doublet coupling can be detected for the 31 P{ 1 H} NMR spectrum of the isotopologue 6' with a 2 J C,P cis ‐coupling of 10 Hz . Compound 6' reveals the expected doublet of triplet pattern in the 13 C{ 1 H} NMR spectrum in the range of iridium(I) bound carbonyl ligands at δ = 174.1 ppm , . A very intense absorption band at 1925 cm –1 for the CO stretch mode can be detected in the IR spectrum of 6 (1878 cm –1 for 6' ) which is well comparable to the known iridium based Vaska type complexes.…”

Iridium Chemistry of 1,6-Bis((tert-butylphosphino)methyl)-1,3,5-cycloheptatriene

“…A triplet at δ −18.6 confirms the presence of an iridium hydride with coupling to the mutually trans phosphorus atoms. Its chemical shift is characteristic of a hydride trans to chlorine, and the size of the 2 J (PH) coupling constant (14.5 Hz) supports the cis position compared to the phosphine groups .…”

Trimeric Cage Complexes of Platinum Group and Coin Metals

“…In contrast to tdppmcy, the resonances of the CH 2 –P carbon nuclei are split into multiplets, which are diagnostic for the interaction of the carbon nuclei with two phosphorus nuclei through one and three bonds. This supports the proposed trans arrangements of the phosphine groups of the tdppmcy ligands 36. Unfortunately, this typical N‐line pattern was only discernible for the gold complex 6 .…”

“…In these cases, the metal centers are blocked for any further metal‐assisted reactions. In the case of the cage compounds reported here, which are generated with polyphosphines, no such additional ligands are needed 27,36. This could allow to perform typical organometallic conversions at the metal site,36 which is a prerequisite for applications in catalysis.…”