Intramolecular Hydrolysis of Coordinated Acetonitrile in a Binuclear Complex of Cobalt(III): X-Ray Crystallographic Analysis of Salts of [(tren)Co(μ-NH2,μ-L)Co(tren)]4+(L=OH, CH3C(O)NH)

Abstract

A synthesis of [( tren )Co(μ-NH2,μ-OH)Co( tren )]4+(3)( tren = tris (2- aminoethyl )amine) is reported along with a series of derivatives: [( tren ) XCo (μ-NH2) CoX ( tren )]n+, where X = CF3SO3- (n = 3)(4), X = CH3CN (n = 5)(5), and [( tren )Co(μ-NH2,μ-CH3C(O)NH)Co( tren )]4+ (6). The substitution of (4) by CH3CN to yield (5) was studied in CH3CN at 20°C, k = 9.0×10-3 s-1, and the intramolecular hydrolysis of (5) to yield the bridging acetamide complex (6) was studied at various acid concentrations. The X-ray crystal structures were determined for (3b) (exafluorophosphate, dihydrate) and (6b) (dithionate, tetrahydrate ). Both crystals are monoclinic, respectively P21/n with a 11.082(2), b 10.402(2), c 15.611(2)Ǻ, β 99.13(2)°, Z 2, and C2/c with a 14.328(2), b 14.046(1), c 16.497(2)Ǻ, β 101.90(1)°, Z 4. For the salt of (3), 2389 data with 1 ≥ 2σ(I) were refined to R 0.070 ( Rw 0.066), and, for the salt of (6), 3087 data with I ≥ 3σ(I) were refined to R 0.041 ( Rw 0.056). Both ions lie on pseudo-symmetric sites involving disorder of the bridging ligands . The structures establish the binding mode of the acetamido ion and the orientation of the tren groups in the isolated complexes.

Modeling Hydrolysis at Dinuclear Iron Centers

“…The observed reactivity supports the proposed mechanism for acetonitrile hydration by dicobalt complexes, 22 where coordinated hydroxide was implicated as the nucleophile but was not directly observed. These results provide insight into what roles the individual metal centers may play in the active site of a bimetallic hydrolase.…”

Unprecedented Inequivalent Metal Coordination Environments in a Mixed‐Ligand Dicobalt Complex

“…The complex has no Co–Co bond given the long intermetal distance of 3.63 Å. This is a consistent feature of ESBO dicobalt(III) complexes, where the intermetal distance is a function of the donor atoms that comprise the {Co 2 X 2 } diamond core, ranging from 2.863(2)–2.951(1) Å for hydroxo‐bridged, 2.885(5)–2.9842(6) Å for alkoxo‐bridged, 2.926(1) Å for imido‐bridged, 2.874(1)–2.977(2) Å for OH – /NH 2 – ‐bridged, to 3.35(1)–3.3441(2) Å with the larger thiolato ligands . Akin to other bimetallic complexes with five chelating ligands, the chirality about each Co center in [ 1 ] 2+ is the same (ΛΛ) for each tris‐chelate Co ion.…”

“…The only exception to this rule for bimetallic complexes with five chelating ligands is [Co 2 (Et 2 dtc) 5 ] 1+ (Et 2 dtc 1– = diethyldithiocarbamato), where the each Co center has an opposing chirality. [27a]…”

Dinuclear 1,4,7-triazacyclononane (tacn) complexes of cobalt(iii) with amido and tacn bridges. Synthesis, characterization and reversible acid-accelerated bridge cleavage

“…The hydrogen atoms on carbon atoms were included in the refinement at idealized positions, whereas all the other hydrogen atoms were included in the refinement as independent atoms. The absolute structure was determined as described by Flack 40 resulting in a Flack parameter of 0.002 (4).…”

“…OH, O 2 , Cl, Br, NO 2 , SO 4 , RCOO, RC(NH) 2 3 and RC(O)NH. 4 The non-bridging ligands in these complexes are typically ammonia or amines like H 2 NCH 2 CH 2 NH 2 or N(CH 2 CH 2 NH 2 ) 3 , 3,4 and e.g. H 2 O, OH − or Cl − may be part of the non-bridging co-ordination sphere.…”