Associative Ligand Exchange and Substrate Activation Reactions by a Zero-Valent Cobalt Tetraisocyanide Complex

Abstract

Tetraisocyanide complex Co(CNAr Mes2 ) 4 (Ar Mes2 = 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ) serves as a crystallographically characterized, thermally stable isocyano analogue of the reactive binary carbonyl Co(CO) 4 . The enhanced stability of Co(CNAr Mes2 ) 4 allows for a systematic investigation of its reactivity profile in an operationally convenient manner, which is not possible for transient Co(CO) 4 . Zerovalent Co(CNAr Mes2 ) 4 undergoes ligand exchange reactions with a variety of 2e − donor, L-type ligands, including triphenylphosphine, tert-butylethylene, and phenylacetylene. Kinetic studies of ligand substitution of Co(CNAr Mes2 ) 4 with phenylacetylene using UV−vis spectroscopy indicates an associative reaction mechanism. This is consistent with the mechanisms proposed for other isolable 17e − transition-metal carbonyls but contrasts with studies proposing zero-valent CoL 4 complexes to react via dissociative reaction pathways. Zerovalent Co(CNAr Mes2 ) 4 also reacts with elemental phosphorus and sulfur and with diphenyl disulfide to form products indicative of multielectron transformations. Under the conditions surveyed, Co(CNAr Mes2 ) 4 did not display 1e − atom-or groupabstraction chemistry. The combined results suggest that this zero-valent, S = 1 / 2 cobalt complex reacts with substrates via associative ligand substitution and inner-sphere multielectron reduction, which is a mode of action that is likely general for this class of Co complexes.

[3+2] Fragmentation of a Pentaphosphido Ligand by Cyanide

“…The mean P−P (2.1361(8) Å) and Co−P (2.300(5) Å) bond lengths in [K(18c‐6)] 5 are similar to those in neutral CoP 3 complexes . The Co−C (1.909(2) Å) and C≡N (1.153(2) Å) bond lengths of the cyanide ligand as well as the CN stretching frequency ( =2068 cm −1 ) are typical for cyanide‐cobalt complexes .…”

“…The tetra‐ n ‐butylammonium salt [ n Bu 4 N] 5 can be isolated in 40–64 % yield by crystallization from toluene. Compared to related neutral species such as [(ArNC) 3 Co(η 3 ‐P 3 )] (Ar=2,6‐(Mes) 2 C 6 H 3 , δ =−276 ppm), and [(CH 3 C(CH 2 PPh 2 ) 3 )Co(η 3 ‐P 3 )] ( δ =−278 ppm), the 31 P{ 1 H} NMR resonance of [ n Bu 4 N] 5 ( δ =−193.2 ppm) is shifted downfield. In addition, the formation of the new cyanodiphoshanide anions [R 2 PPCN] − ( 6‐R , R=Cy, t Bu, Ph, N( i Pr) 2 ) was observed, which were identified by the characteristic set of doublets ( 1 J PP =261 to 278 Hz) in the 31 P{ 1 H} NMR spectra.…”

“…Monitoring the reaction by 31 P{ 1 H} NMR spectroscopy revealed the clean formation of [(PHDI)Co-(h 3 -P 3 )(CN)] À (5;s inglet at d = À193.2 ppm), which is av ery rare example of an anionic cyclo-P 3 cobalt complex. [16] The tetra-n-butylammonium salt [nBu 4 N]5 can be isolated in 40-64 %y ield by crystallization from toluene.C ompared to related neutral species such as [(ArNC) 3 Co(h 3 -P 3 )] (Ar = 2,6-(Mes) 2 C 6 H 3 , d = À276 ppm), [17] and [(CH 3 C(CH 2 PPh 2 ) 3 )Co-(h 3 -P 3 )] (d = À278 ppm), [18] the 31 P{ 1 H} NMR resonance of [nBu 4 N]5 (d = À193.2 ppm) is shifted downfield. In addition, the formation of the new cyanodiphoshanide anions [R 2 PPCN] À (6-R,R = Cy, tBu, Ph, N(iPr) 2 )w as observed, which were identified by the characteristic set of doublets ( 1 J PP = 261 to 278 Hz) in the 31 P{ 1 H} NMR spectra.…”

“…Themean PÀP(2.1361(8) )and CoÀP(2.300(5) )bond lengths in [K(18c-6)]5 are similar to those in neutral CoP 3 complexes. [16][17][18]21] TheC o ÀC( 1.909(2) )a nd CN( 1.153-(2) )b ond lengths of the cyanide ligand as well as the CN stretching frequency (ñ = 2068 cm À1 )a re typical for cyanidecobalt complexes. [22] Thes olid-state molecular structure of [K(18c-6)]6-tBu shows an almost linear, phosphanyl-substituted PCN moiety (P1-C1-N1 178.4(1)8 8)with aP ÀPdistance of 2.1895(4) ,t hat is,c lose to at ypical single bond.…”

Ringkontraktion durch NHC‐induzierte Pnictogen‐Abstraktion

“…Diese Abstände unterscheiden sich geringfügig von denen des unlängst publizierten neutralen Komplexes [{CNAr Mes2 } 3 Co(h 3 -P 3 )] (Ar Mes2 = 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ), bei dem die Co-P-Bindungslängen mit 2.312(1) bis zu 2.317(1) etwas verlängert sind. [14] Da wir an der Klärung des Reaktionsverlaufs zwischen 1 und Me NHC interessiert waren, führten wir eine temperaturabhängige 31 P-NMR-Untersuchung im Bereich von À80 8 8C bis Raumtemperatur (in 20 8 8C-Schritten) durch. Die Spektren zeigen mehrere Signalsätze,d ie auf die Bildung von unterschiedlichen Intermediaten hinweisen.…”