A Less Carbocentric View of Agostic Interactions:  The Complexes [Rh(η⁴-cod){H₂A(mt)₂}] (A = B, C⁺; mt = Methimazolyl)

Abstract

The reaction of [Rh 2 (µ-Cl) 2 (cod) 2 ] (cod ) 1,5-cyclooctadiene) with Na[H 2 B(mt) 2 ] (mt ) methimazolyl) provides the complex [Rh(cod){H 2 B(mt) 2 }] (1), which in turn reacts with CO or CNC 6 H 3 Me 2 -2,6 to provide the derivatives [RhL 2 {H 2 B(mt) 2 }] (L ) CO (2), CNC 6 H 3 Me 2 -2,6 (3)). In a similar manner [Rh 2 -(µ-Cl) 2 (cod) 2 ] reacts with H 2 C(mt) 2 to provide the cationic complex [Rh(cod){H 2 C(mt) 2 }] + (4 + ), which was isolated after counteranion metathesis as either 4‚BF 4 or 4‚PF 6 . Carbonylation of 4‚PF 6 provides [Rh(CO) 2 {H 2 C(mt) 2 }]PF 6 (5‚PF 6 ); however, the reaction is reversible in the presence of cod, regenerating 4‚PF 6 under reduced pressure. The reactions of 4‚PF 6 with CNC 6 H 3 Me 2 -2,6 or CNCMe 3 provide respectively the salts [Rh(CNC 6 H 3 Me 2 -2,6) 2 {H 2 C(mt) 2 }]PF 6 (6‚PF 6 ) and [Rh(CNCMe 3 ) 4 ]PF 6 . The crystal structures of 1, 4‚BF 4 , 4‚PF 6 , and 6‚BF 4 reveal long B-H‚‚‚Rh or C-H‚‚‚Rh interactions; however, such an interaction is effectively absent for 5‚PF 6 ‚CHCl 3 , while solution spectroscopy ( 1 H NMR and IR) indicates that none of these interactions persist in solution. The complexes 1 and 4 + represent the first structurally characterized isoelectronic pair involving, albeit weak, three-center-two-electron B-Hmetal or C-H-metal interactions.

Design, Synthesis, and Chemistry of Bis(σ)borate and Agostic Complexes of Group 7 Metals

“…Due to their important role in metal‐catalyzed B−H activation, a great deal of attention has been devoted to σ‐borate and B‐agostic complexes . As a result, several σ‐borane and hydridoborate complexes have been isolated and structurally characterized by several groups, including those of Hartwig, Hill, Weller, Bourissou, Sabo‐Etienne, and others…”

Enhancing Reactivity of Directly íObservable B–H–Pt Interactions through Conformational Rigidity

“…In particular, polypyrazolylborate complexes of group 10 metals have been widely employed in a variety of catalytic applications. With respect to stabilizing high‐valent platinum(IV) complexes, bis(pyrazolyl)dihydridoborate (Bp) or bis(3,5‐dimethylpyrazolyl)dihydridoborate (Bp*) is an interesting choice: the B–H fragment might serve as a weakly coordinating pseudo‐axial ligand, such as in A (Scheme ), which allows direct observation of B–H–Pt interactions. Reductive elimination from hydrido hydrocarbylplatinum(IV) intermediates such as B (R = H), is interesting since it provides proof‐of‐concept for the microscopic reverse: C–H activation at a Pt II center.…”

Lead(II) in a sulfur-rich environment: Synthesis and molecular structure of the first dinuclear bis(mercaptoimidazolyl)methane complex

“…1). Significantly, although the structures of a few mononuclear [12][13][14] and multinuclear [7,8,15] Bmm Me derivatives have been reported, [Pb 2 (Bmm Me ) 5 ] 4+ appears to be the first dinuclear complex to be structurally characterized for this ligand.…”