Mixed-Metal Cluster Chemistry. 2.¹ Site-Selective Substitution of CpWIr₃(CO)₁₁ by Phosphines:  X-ray Crystal Structures of CpWIr₃(μ-CO)₃(CO)₇(PPh₃), CpWIr₃(μ-CO)₃(CO)₆(PPh₃)₂, and CpWIr₃(μ-CO)₃(CO)₇(PMe₃)

Abstract

Reactions of CpWIr 3 (CO) 11 (1) with stoichiometric amounts of phosphines afford siteselective products CpWIr 3 (µ-CO) 3 (CO) 8-x (L) x (L ) PPh 3 , x ) 1 (2), 2 (3), or 3 (4); L ) PMe 3 , x ) 1 (5), 2 (6), or 3 (7)) in fair to excellent yields (38-63%). These products exhibit ligand fluxionality in solution, resolvable at low temperature into the constituent interconverting isomers. The structures of three of the species, namely 2a, 3a, and 5a, have been determined by X-ray diffraction studies. The single-crystal X-ray studies reveal that ligand substitution induces a rearrangement in the cluster coordination sphere from the all-terminal carbonyl ligand geometry of CpWIr 3 (CO) 11 to one in which the three edges of a WIr 2 face of the tetrahedral core contain bridging carbonyls (2a, 3a) or one in which the three edges of the triiridium face are bridged by carbonyl ligands (5a). The triphenylphosphine in 2a ligates radially to the carbonyl-bridged WIr 2 face; a similar site for one of the phosphines is found in 3a, with the second triphenylphosphine coordinated in an axial position with respect to this face. The trimethylphosphine ligand in 5a is located in an axial site with respect to the basal carbonyl-bridged triiridium plane. Information from the crystallographicallyverified isomers, the ligand substitution pattern in the related tetrairidium system, and chemical shifts of signals in the 31 P NMR spectra has been used to suggest coordination geometries for the isomeric forms of the complexes above and for other reported derivatives.

Mixed-Metal Cluster Chemistry. 11.1Reactions of Tungsten−Iridium Clusters with Terminal Alkynes and Tungsten Acetylides: X-ray Crystal Structures of Cp2W2Ir2(μ4-η2-HC2Ph)(μ-CO)4(CO)4and Cp2W2Ir3(μ4-η2-C2C6H4Me-4)(μ-CO)(CO)9

“…The chemistry of mixed-metal clusters has been of enduring interest. − Mixed-metal clusters are potential precursors to supported bimetallic catalysts, the differing metals provide effective labels for ligand fluxionality studies, and the varying metals of the cluster core afford the possibility of metallo- and bond-selectivity and thus directing reactivity for a range of reagents. We have probed the last-mentioned feature utilizing phosphines and the systematically varied series of tetrahedral clusters Cp x M x Ir 4 - x (CO) 12 - x ( x = 0−2, M = W, Mo) − noting enhanced reactivity and differing site-selectivity and carbonyl fluxionality upon heterometal incorporation into the “parent” cluster Ir 4 (CO) 12 .…”

Mixed-metal cluster chemistry. 26 . Proclivity for “all-terminal” or “plane-of-bridging-carbonyls” ligand disposition in tungsten–triiridium clusters

“…The plane of bridging carbonyls about a WIr 2 face is in contrast to the crystallographically-reported all-terminal structures of analogous clusters with methylcyclopentadienyl [15] and cyclopentadienyl [12,16] ligands and a carbonyl substitution derivative of the former with two CNC 6 H 3 Me 2 -2,6 ligands [9], but a plane of bridging carbonyls about a WIr 2 face is also seen in the structure of the cyclopentadienyl-containing derivative where one of the carbonyl groups is replaced by PPh 3 [5] or P(OMe) 3 [17], or two of the carbonyls are replaced by P(OPh) 3 [7], or the methylcyclopentadienyl derivative where one carbonyl is replaced by PMe 3 [10], ligand replacements that increase electron donation to the cluster. Note that a plane of bridging carbonyls about the Ir 3 face is seen in the structures of cyclopentadienyl-containing derivatives where one of the carbonyls is replaced by PMe 3 [5] or P(OMe) 3 [8], or where two of the carbonyls are replaced by an Ir-Ir bridging bidentate diphosphine (bis(diphenylphosphino)methane, dppm; 1,2-bis(diphenylphosphino)ethane, dppe; bis(diphenylphosphino)acetylene, dppa) [4]. In all instances, a plane of bridging carbonyls is observed upon introduction of a sufficiently strongly electron-donating ligand.…”

“…We have prepared a significant number of phosphine and isonitrile derivatives of these clusters [4][5][6][7][8][9][10][11] and, while all crystallographically-confirmed molybdenum-containing Journal of Organometallic Chemistry 689 (2004) 50-57 www.elsevier.com/locate/jorganchem clusters possess a MIr 2 plane of bridging carbonyls, crystallographically-verified tungsten-containing examples possess all-terminal or plane-of-bridging-carbonyls configurations, depending on the ligand set. We report herein the synthesis and crystallographic characterization of WIr 3 (l-CO) 3 (CO) 8 (g-C 5 Me 5 ), for which permethylation of the cyclopentadienyl ligand is sufficient to modify the carbonyl disposition in the ground state structure, together with a DFT study exploring the proclivity of these mixed group 6-iridium tetrahedral clusters to adopt the two carbonyl ligand arrangements, and studies of ligand fluxionality at WIr 3 (CO) 11 (g-C 5 H 5 ) and the related tetrahedral cluster W 2 Ir 2 (CO) 10 (g-C 5 H 5 ) 2 .…”

Mixed-Metal Cluster Chemistry. 13. Syntheses and Isomer Distribution Studies of Cp2W2Ir2(μ-CO)3(CO)7-n(PR3)n(n= 1, 2; R = Ph, Me): X-ray Crystal Structure of Cp2W2Ir2(μ-CO)3(CO)6(PPh3)

“…Six terminal carbonyl ligands and an iridium-ligated triphenylphosphine ligand complete the coordination sphere. The W 2 Ir 2 core distances (W−Ir av = 2.866 Å, W−W = 3.0604(6) Å, Ir−Ir = 2.7348(6) Å) are all slightly longer than those of 1 (W−Ir av = 2.835 Å, W−W = 2.991(1) Å, Ir−Ir = 2.722(1) Å); core distances of the related mono(phosphine)-substituted tungsten−triiridium clusters CpWIr 3 (μ-CO) 3 (CO) 7 (L) (L = PPh 3 , PMe 3 , PMe 2 Ph) compared to those of the precursor CpWIr 3 (CO) 11 are also consistent with core expansion upon introduction of P-donor ligands. Intracore bond angles are all close to 60° as expected.…”

“…The tetrahedral mixed-metal clusters CpWIr 3 (CO) 11 and Cp 2 W 2 Ir 2 (CO) 10 ( 1 ) are conceptually derived from Ir 4 (CO) 12 by successive replacement of Ir(CO) 3 vertexes with one or two CpW(CO) 2 units and, in comparison to the iridium−rhodium clusters, incorporate the significantly more electropositive metal tungsten. We have previously reported the synthesis and characterization of ligand-substituted derivatives of CpWIr 3 (CO) 11 , namely CpWIr 3 (μ-CO) 3 (CO) 8 - n (L) n (L = PPh 3 , PMe 3 ; n = 1−3), and have recently reported the isomer distribution at these clusters . The electropositive tungsten did not appear to polarize the electron distribution toward the iridium atoms, as may have been expected; the WIr 2 -bridged form was predominant across the isomers of CpWIr 3 (μ-CO) 3 (CO) 8 - n (L) n , whereas an Ir 3 basal plane is expected if the electron distribution is polarized toward the iridium atoms.…”