Phosphine derivatives of the 4-methylquinoline triosmium cluster [(μ-H)Os3(CO)10{μ-1,2-η2-C9H5(CH3)N}]: crystal structures of two isomeric compounds [(μ-H)Os3(CO)9{μ-1,2-η2-C9H5(CH3)N}(PPh3)] and [(μ-H)Os3(CO)9{μ-1,2-η2-C9H5(CH3)N}{P(OMe)3}]

Experimental and computational preference for phosphine regioselectivity and stereoselective tripodal rotation in HOs3(CO)8(PPh3)2(μ-1,2-N,C-η1,κ1-C7H4NS)

“…In this scenario, the P– –Os atoms display an obtuse angle, a feature underscored by numerous structural studies involving related trimetallic clusters where the P– –Os bond angle ranges from 105–117°. 14,16–18,24 The computed P– –Os bond angle in D1 is 109°. Assuming a fixed cluster polyhedron, expansion of the P– –Os bond angle in D1 effectively permutes the PPh 3 ligand to the other equatorial site at the nitrogen-substituted osmium center.…”

“…The Os(1)–P(1) [2.3888(11) Å], Os(1)–N(1) [2.138(4) Å], and Os(2)–C(10) [2.086(5) Å] bond distances involving the ancillary ligands are similar to those reported by us in related trisosmium clusters. 14,18,20 However, the locus of PPh 3 substitution in 2 is quite different from that displayed in the 4-methylquinolinate analogues HOs 3 (CO) 9 (PPh 3 )[μ-1,2-η 1 ,κ 1 -C 9 H 5 (CH 3 )N] and HOs 3 (CO) 9 [P(OMe) 3 ][μ-1,2-η 1 ,κ 1 -C 9 H 5 (CH 3 )N]. 14 The pnictogen ligand in these latter derivatives occupies an equatorial site at the non-metalated osmium atom.…”

“… 14,18,20 However, the locus of PPh 3 substitution in 2 is quite different from that displayed in the 4-methylquinolinate analogues HOs 3 (CO) 9 (PPh 3 )[μ-1,2-η 1 ,κ 1 -C 9 H 5 (CH 3 )N] and HOs 3 (CO) 9 [P(OMe) 3 ][μ-1,2-η 1 ,κ 1 -C 9 H 5 (CH 3 )N]. 14 The pnictogen ligand in these latter derivatives occupies an equatorial site at the non-metalated osmium atom. The different regiochemistry for phosphine substitution in the current cluster that contains a π-excessive heterocycle versus our earlier report on the Os 3 cluster with a π-deficient heterocycle is striking and underscores the importance of the metalated platform in controlling the outcome of the reaction.…”

“… 25 Syn positioning of the phosphine to the hydride-bridged metal–metal bond in other clusters does not always represent the thermodynamically favored regiochemistry for this pair of ligands. 14 We suspect that in such cases any beneficial orbital effect involving the hydrogen and the electrons in the P–Os bond is counterbalanced by extant steric perturbations within the molecule. The hydride regiochemistry displayed in this genre of metal clusters cannot be generalized with certainty at this time and must be evaluated on a case by case basis.…”

“…6 c In comparison to numerous studies involving the 1,8 isomer, the corresponding 1,2 isomer has received relatively little attention. 14 …”