Susan M. Waterman

“Very mixed”-metal carbonyl clusters

Publisher Summary The multi-metallic coordination of organic molecules at clusters facilitates substrate transformations not readily achievable at mononuclear complexes. The aggregation of metal atoms within a metal cluster core can afford molecules with a large number of accessible oxidation states which may have the potential to function as electron reservoirs. A significant number of mixed-metal clusters contain metals from the same group or adjacent groups, but far fewer mixed-metal clusters incorporating disparate metals have been reported. The presence of differing metals introduces the possibility of metallo-selectivity into ligand substitution. This selectivity should be enhanced upon accentuating the disparity between the metals. The introduction of differing metals into a cluster core also reduces the effective symmetry over that of related homo-metallic clusters, rendering coordination sites for incoming ligands inequivalent and affording the prospect of site- as well as metallo-selectivity.

Mixed-metal cluster chemistry XII: isocyanide derivatives of [CpWIr3(CO)11]; X-ray crystal structure of [CpWIr3(CO)9(CNC6H3Me2-2,6)2]

Abstract Reactions of [CpWIr 3 (CO) 11 ] ( 1 ) with stoichiometric amounts of isocyanides afford the clusters [CpWIr 3 (CO) 11− n (CNR) n ] [R=Xy (C 6 H 3 Me 2 -2,6), n =1 ( 2 ), 2 ( 3 ), 3 ( 4 ); R= t Bu, n =1 ( 5 ), 2 ( 6 ), 3 ( 7 )] in good to excellent yields (47–63%). The products exhibit ligand fluxionality in solution, with the 13 C-NMR spectra of 4 - 6 revealing that the carbonyls are undergoing fast exchange at 143 K. A single-crystal X-ray study of [CpWIr 3 (CO) 9 (CNXy) 2 ] ( 3 ) reveals that the coordination sphere of the cluster has an all-terminal ligand geometry, the first for a ligand substituted derivative of 1 . The two iridium-ligated 2,6-dimethylphenylisocyanide ligands are coordinated to the same iridium vertex, the second example of this coordination geometry for a transition metal cluster.

Mixed-metal cluster chemistry VIII1: phosphite substitution at [CpWIr3(CO)11]; X-ray crystal structure of [CpWIr3(μ-CO)3(CO)6{P(OPh)3}2]

Reactions of [CpWIr 3 (CO) 11 ] ( 1 ) with stoichiometric amounts of phosphites afford the substitution products [CpWIr 3 ( μ -CO) 3 (CO) 8- n (L) n ] [L=P(OMe) 3 , n =1 ( 2 ), 2 ( 3 ), 3 ( 4 ); L=P(OPh) 3 , n =1 ( 5 ), 2 ( 6 ), 3 ( 7 )] in fair to excellent yields (29–71%). Clusters 2 , 4 , 5 and 7 are fluxional in solution, with the interconverting isomers resolvable at low temperatures. A structural study of 6 reveals that the three edges of a WIr 2 face of the tetrahedral core are spanned by bridging carbonyls, and that iridium-bound triphenylphosphites ligate radially and axially and the tungsten-bound cyclopentadienyl coordinates axially with respect to this WIr 2 face. Information from this crystal structure, 31 P-NMR data, and results with analogous triphenylphosphine-ligated tungsten–triiridium clusters have been employed to suggest coordination geometries for the isomers.

Mixed-metal cluster chemistry IX: alkylarylphosphine derivatives of [CpWIr3(CO)11] and X-ray crystal structure of [CpWIr3(μ-CO)3(CO)7(PMe2Ph)]

Abstract Reactions of [CpWIr 3 (CO) 11 ] ( 1 ) with equimolar amounts of the bidentate alkylarylphosphines bis(diphenylphosphino)ethane (dppe) and bis(diphenylphosphino)methane (dppm) afford the substitution products [CpWIr 3 ( μ -L)( μ -CO) 3 (CO) 6 ] [L=dppe ( 2 ), dppm ( 3 )]. Reactions of 1 with stoichiometric amounts of the monodentate alkylarylphosphines PMePh 2 and PMe 2 Ph afford the substitution products [CpWIr 3 ( μ -CO) 3 (CO) 8- n (L) n ] [L=PMePh 2 , n =1 ( 4 ), 2 ( 5 ), 3 ( 6 ); L=PMe 2 Ph, n =1 ( 7 ), 2 ( 8 ), 3 ( 9 )]. The clusters 2–8 are fluxional in solution, with the interconverting isomers resolvable at low temperatures. Variable temperature 31 P- and 13 C-NMR spectra for 2 and 3 enable structural assignment of the isomers, revealing a triiridium face spanned by bridging carbonyls, a diaxially-ligated diphosphine with (in the case of dppe) a flexible backbone, and an apical tungsten-coordinated cyclopentadienyl (Cp) ligand situated over differing WIr 2 faces in the configurations. 13 C-NMR exchange spectroscopy (EXSY) spectra reveal that these isomers interconvert by tripodal rotation at the apical CpW(CO) 2 , resolvable (in the case of 3 ) into a ‘waggling’ of the CpW(CO) 2 group over the non-diphosphine ligated WIr 2 faces before the onset of complete tripodal rotation. A ‘merry-go-round’ of carbonyl ligands in the basal Ir( μ -CO) 3 (CO) 3 plane occurs at a similar temperature to that of tripodal rotation for 3 , but at a higher temperature for 2 . For 2 , flexing of the diphosphine backbone is the highest energy process observed. A structural study of one isomer of 7 , namely 7a , reveals that the three edges of the triiridium face of the tetrahedral core are spanned by bridging carbonyls, and that the iridium-bound PMe 2 Ph ligates axially and the tungsten-bound Cp coordinates apically with respect to the triiridium face. Information from this crystal structure, 31 P-NMR data, and comparison with analogous PPh 3 - and PMe 3 -ligated tungsten–triiridium clusters have been employed to suggest coordination geometries for the other isomers of 4–9 . The geometries of the PMePh 2 - and PMe 2 Ph-derivatives 4-9 follow those of the previously reported PMe 3 -derivatives, with the exception of the minor isomer [CpWIr 3 ( μ -CO) 3 (CO) 5 (PMePh 2 ) 3 ] ( 6b ) which has an unprecedented triradial, apical substitution geometry.

Mixed-metal cluster chemistry III .PC activation at tungsten-triiridium cores; X-ray crystal structures of [CpwIr3{μ3-η2-PPh(C6H4})(μ-CO)2(CO)7] and [CpWIr3{μ3-η2-PPh(C6H4)}(μ-CO)2(CO)6(PPh3)]

The thermolysis of [CpWIr3(μ-CO)3(CO)7(PPh3)] in refluxing toluene gives [CpWIr3{μ3-η2-PPh(C6H4)}(μ-CO)2(CO)7] (1) in good yield (56%), together with [CpWIr3(CO)11] (2) (32%); an analogous reaction with [CpWIr3(μ-CO)3(CO)6(PPh3)2] gives 1 (23%) and [CpWIr3(μ3-η2-PPh(C6H4)}(μ-CO)2(CO)6(PPh3)] (3) (39%). Products 1 and 3 (in 15 and 44% yield respectively) are also obtained from heating [CpWIr3(μ-Co)3(CO)5(PPh3)7]. Both 1 and 3 have been structurally characterized. The structural studies show that orthometallation has occurred, to afford products with (phenylphosphido)phenyl-P,C ligands capping the triiridium faces. In 3, the intact PPh3 resides at an iridium ligated by the phosphorus of the capping group. Attempts to effect further PC cleavage of 1 (pyrolysis, photolysis, reaction with trimethylamine-N-oxide) were unsuccessful, as were attempts to effect CH activation at the analogous [CpWIr3(μ-CO)3(CO)7(PMe3)].

Mixed-metal cluster chemistry 14: Reaction of [Cp2W2Ir2(CO)10] with trimethylphosphite; X-ray crystal structures of [Cp2W2Ir2(m-CO)3(CO)5{P(OMe)3}2] and two modifications of [CpWIr3(m-CO)3(CO)7{P(OMe)3}]

Abstract Reactions of [Cp 2 W 2 Ir 2 (CO) 10 ] with stoichiometric amounts of trimethylphosphite afford the substitution products [Cp 2 W 2 Ir 2 (μ-CO) 3 (CO) 7− n {P(OMe) 3 } n ] [ n =1 ( 2 ) or 2 ( 3 )]. A structural study of 3 reveals that the three edges of a WIr 2 face of the tetrahedral core are spanned by bridging carbonyls, and that the iridium-bound P(OMe) 3 groups ligate radially and axially with respect to the plane of bridging carbonyls. The tungsten-bound η 5 -cyclopentadienyl groups ligate axially and apically with respect to the plane of bridging carbonyls. An unusual decomposition reaction was observed during the crystallization of 3 . A single-crystal X-ray study from the second type of crystals from a solution of 3 was identified as the previously synthesized [CpWIr 3 (μ-CO) 3 (CO) 7 {P(OMe) 3 }] ( 4 ). A structural study of 4 reveals that the cluster core has a WIr 3 tetrahedral framework, with three edges of a WIr 2 face spanned by bridging carbonyls and that the iridium-bound P(OMe) 3 and the tungsten-bound η 5 -cyclopentadienyl moieties ligate diaxially with respect to the plane of bridging carbonyls. Monitoring a solution of 3 by 31 P-NMR spectroscopy reveals slow formation of 4 (93% 3 : 7% 4 over 4 days) at room temperature. One configuration only of clusters 2 and 3 was observed in the 13 C- and 31 P-NMR spectra (between 183 and 303 K), with no evidence for the presence of additional isomers undergoing very fast exchange. The NMR spectra of 3 are consistent with the formulation given in the X-ray crystallographic study. The NMR spectra of 2 suggest a configuration with axial phosphite, axial Cp, apical Cp, analogous to the related clusters [Cp 2 M 2 Ir 2 (μ-CO) 3 (CO) 6 (PMe 3 )] (M=Mo, W), the molybdenum analogue of which has been structurally characterized previously.

High nuclearity ruthenium carbonyl cluster chemistry VII. Synthesis, NMR studies, electrochemistry and X-ray crystal structure of [PPN] [Ru8(μ8-P)(CO)22]

The reaction between [Ru3(μ-H)(μ-NC5H4)(CO)10] and chlorodiphenylphosphine in refluxing chlorobenzene, followed by metathesis with bis(triphenylphosphoranylidene)ammonium chloride ([PPN]Cl), affords [PPN][Ru8(μ8-P)(CO)22] (1) in around 30% yield. 31P-NMR solution spectra are consistent with the presence of at least two isomers of the cluster anion, presumably due to differing carbonyl distributions; the chemical shifts for these configurations (600–800 ppm downfield of H3PO4) are consistent with a highly deshielded interstitial phosphorus atom. An X-ray structural study of one isomer of 1 reveals that the phosphorus atom occupies an interstitial square antiprismatic site defined by the eight ruthenium atoms, with two bridging carbonyl ligands on opposite faces spanning interplanar Ru–Ru bonds, and twenty terminal carbonyl ligands completing the ligand set. The solid state 31P-NMR spectrum of the crystallographically-identified isomer reveals a signal at 596.1 ppm assigned to the square antiprismatic interstitial phosphorus atom. Formal electron counting suggests that 1 has four electrons less than expected using Wades rules. The reductive electrochemistry of 1 has been examined by cyclic voltammetry, and reveals the presence of two one-electron and one two-electron reduction waves, an uptake of four electrons in total, consistent with the clusters theoretical electron deficiency in the resting state.

Mixed-metal cluster chemistry 15: some bidentate phosphine chemistry of tungsten–iridium clusters

Abstract Reactions of [Cp2W2Ir2(CO)10] (4) with equimolar amounts of the bidentate phosphines bis(diphenylphosphino)methane (dppm) and 1,2-bis(diphenylphosphino)ethane (dppe) afford the substitution products [Cp2W2Ir2(μ-CO)3(μ-L)(CO)5] [L=dppm (5), dppe (6)] in excellent yields (76% and 80%, respectively). The clusters 5 and 6 are fluxional in solution, with the interconverting isomers of 6 resolvable at low temperatures. Variable-temperature 31P- and 13C-NMR for 5 and 6 enable structural assignment of the isomers. 13C-NMR exchange spectroscopy (EXSY) spectra reveal that the fluxional process observed with 5, and which interconverts the isomers of 6, involves a ‘waggling’ of the CpW(CO)2 group over the W2Ir faces or complete tripodal rotation at the apical CpW(CO)2. Reaction of [CpWIr3(CO)11] (1) with an equimolar amount of the bidentate phosphine 1,2-bis(diphenylphosphino)benzene (pdpp) affords the substitution product [CpWIr3(μ-CO)3(μ-pdpp)(CO)6] (7) in reasonable yield (62%). Spectroscopic data suggest 7 adopts one configuration in solution, in contrast to the two configurations observed with [CpWIr3(μ-CO)3(μ-L)(CO)6] [L=dppe (2), dppm (3)], a result ascribed to the inflexible diphosphine backbone.