A Well-Defined Isocyano Analogue of HCo(CO)₄. 1: Synthesis, Decomposition, and Catalytic 1,1-Hydrogenation of Isocyanides

Abstract

Reported here is the synthesis and characterization of the tetrakis­(m-terphenyl isocyanide)cobalt hydride HCo­(CNArMes2)4 (1; ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3). Monohydride 1 serves as a well-defined isocyano analogue of the tetracarbonyl hydride HCo­(CO)4. While tetrakis-phosphine analogues of HCo­(CO)4 have been reported previously, these compounds have failed to exhibit a reactivity profile that can be compared and contrasted with HCo­(CO)4 in a systematic fashion. Herein, HCo­(CNArMes2)4 (1) is shown to be a readily accessed and reactive complex that allows for this comparison. For example, HCo­(CNArMes2)4 (1) is found to decompose smoothly to the κ1 -C-iminoformyl complex Co­(η6-(Mes)-κ1 C-C­(H)­NArMes2)­(CNArMes2) (2). Kinetic analysis of this decomposition and that of the d 1-isotopomer DCo­(CNArMes2)4 (1-d 1) revealed a unimolecular process characterized by a large primary k H/ k D isotope effect (3.2(6)) and no dependence on the presence of free CNArMes2. These data point to rate-limiting hydride α-migration and formation of the κ1-C-iminoformyl species [Co­(κ1-C-C­(H)NArMes2)­(CNArMes2)3] as a critical intermediate. Indeed, ligand substitution reactions of HCo­(CNArMes2)4 (1), as well as 13C-labeling experiments of the decomposition product 2, demonstrate that hydride α-migration is the dominant mechanistic feature of this system. Most notably, this behavior is in contrast with that of HCo­(CO)4, for which it has been established that CO ligand dissociation is the initial mechanistic feature. Additional support for the critical role of hydride α-migration in HCo­(CNArMes2)4 (1) was obtained by the development of catalytic CNArMes2 1,1-hydrogenation to form a stable and isolable methylenimine.

Aminomethyl Transfer (Mannich) Reactions Between an O‐Triethylsilylated Hemiaminal and Anilines, RnC6H5−nNH2 Leading to New Diamines, Triamines, Imines, or 1,3,5‐Triazines Dependent upon Substituent R

“…The only other such imine structurer eported, also with ab ulky substituent on nitrogen, CH 2 =NAr (Ar = 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ), also exhibits as imilar NH 2 group orthogonal to the aryl group with as imilar CÀN methylene bond length of 1.247 . [15] In both the reported imine and ours, the methylene protons can be noted by 1 HNMR spectroscopy as ap air of doublets, for 4 at 6.12 ( 1 J HH = 18 Hz) and 7.13 ppm ( 1 J HH = 12 Hz), respectively.I mine 4,u nlike the previously reported example, is av ery thermally and oxida-tively stable materiala nd its possible chemicalr eactivity is currently under investigation.…”

Ta(CNDipp)6: An Isocyanide Analogue of Hexacarbonyltantalum(0)

“…But unlike HTa(PF 3 ) 6 which is fairly robust, no evidence for the isocyanide hydride was obtained. Isocyanide metal hydrides are rare species and Figueroa and co‐workers recently reported [HFe(CNAr′) 4 ] −[31a] and [HCo(CNAr′) 4 ] …”

Substitution and Redox Properties of Some Organoisocyanide Cobalt(II) Complexes

“…Earlier studies showed that these pentakis and tetrakis cobalt(II) complexes react with amines to undergo reduction to their 4 ] in the À1, 0, and +1 oxidation states were synthesized a few years back [29] using m-terphenyl isocyanide as the stabilizing ligand. The same ligand was later employed in the synthesis of the isocyano counterpart of HCo(CO) 4 followed by a study of its decomposition and catalytic hydrogenation [30]. Figueroa and co-workers [31] most recently synthesized some isocyanide palladium(0) complexes as catalysts for the SuzukiMiyaura cross-coupling of aryl bromides and arylboronic acids.…”