Mixed-metal cluster chemistry

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

“…Our results ultimately reveal the same type of trend as Calhorda and co-workers [20,21] have reported in DFT calculations on M 2 (CO) 9 and M 3 (CO) 12 clusters, where M ¼ Fe, Ru, or Os. In their calculations (on smaller clusters than those investigated here, with many wellcharacterized crystallographic structures amongst the species surveyed) they found a consistent tendency towards carbonyl bridging in Fe-containing clusters, and towards terminal carbonyl ligation in clusters dominated by Os.…”

“…The cluster is electron precise, with 60 [6(W) + 3 Â 9(Ir) + 5(g-C 5 Me 5 ) + 11 Â 2(CO)] cluster valence electrons. 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].…”

“…Clusters of the lighter metals (Co, Rh) possess crystallographically-defined M 4 (l-CO) 3 (CO) 9 ground-state structures with a plane of bridging carbonyls, whereas the corresponding cluster of the heaviest metal (Ir) adopts an all-terminal carbonyl disposition in the crystallographically-observed ground state. The interconversion of these two configurations is important as a critical feature of the Cotton merry-goround mechanism rationalizing aspects of carbonyl fluxionality in this class of cluster.…”

“…The interconversion of these two configurations is important as a critical feature of the Cotton merry-goround mechanism rationalizing aspects of carbonyl fluxionality in this class of cluster. The relative stability of the two configurations is clearly of interest, density functional theory (DFT) calculations on Rh 4 (l-CO) 3 (CO) 9 (plane-of-bridging-carbonyls) and Rh 4 (CO) 12 (all-terminal) in the gas phase confirming the bridged conformation as the more stable for the rhodium cluster (by 55 kJ mol À1 ) [3].…”

“…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 .…”