A Silyl-Nickel Moiety as a Metal–Ligand Cooperative Site

Abstract

Nickel(II) complexes supported by a diphosphinosilyl ligand, [PhSi(2-P i Pr 2 C 6 H 4 ) 2 ] − (PhSiP 2 ), reveal unusual metal−ligand cooperativity (MLC). While (PhSiP 2 )-Ni(NHMes) (2a) was cleanly isolated at room temperature, a nickel triisopropylphenylamido species, (PhSiP 2 )Ni(NHTrip) (2b), slowly transformed into a nickel(II) phenyl species, [(ArNH)SiP 2 ]Ni(Ph) (3b), where (ArNH)SiP 2 − = [(NHTrip)Si(2-P i Pr 2 C 6 H 4 ) 2 ] − . The X-ray crystallographic data of 3b exhibit a Si−N bond generated from Si−N coupling between the silyl moiety and amino group, along with cleavage of a Si−C bond. Because substoichiometric amounts of π-acidic ligands, such as isocyanide, enhance the conversion rate of 2 to 3 (k obs = 0.28 vs 0.44 h −1 ), this reaction may involve reductive elimination (RE) and oxidative addition (OA) operating at the silyl-nickel moiety. This is further supported by the fact that the presence of excess π-acidic ligands results in the generation of demetalated ligands (ArNH)PhSiP 2 (4) having both Si−N and Si−Ph bonds and the nickel(0) species. Theoretical evaluations also agree on such a pathway. Interestingly, the reaction of a nickel phenyl species (3) with gaseous carbon dioxide (CO 2 (g)) produces a nickel(II) carbamato complex, (PhSiP 2 )Ni(OC(O)NHAr) (6), which may involve a RE−OA process occurring at a nickel center. Although 2 and 3 might be in equilibrium, the reaction of 3 with CO 2 does not follow this pathway. Instead, a CO 2 interaction induces RE at the silyl-nickel moiety, followed by amide group transfer, to give a carbamato product, 6, based on our experimental and theoretical evaluations. These results highly support that group transfer involving MLC can be managed via a RE−OA pathway at the silyl-nickel(II) moiety.

Recent Advances in the Chemistry of Metal Carbamates

“…The scenario changed over the last 15 years, as several carbamato complexes obtained by this methodology were reported, and especially organometallic species. These include late d-block metals such as iridium [190,191], nickel [192][193][194][195][196][197], palladium [198,199], gold [200] and zinc [201][202][203][204], f-block metals cerium [134] and uranium [205][206][207][208][209] and p-block metals tin [210] and gallium [211,212]. Furthermore, in situ-formed amide complex of Zn(II) and alkyl-amide of Mg(II) were mixed under carbon dioxide atmosphere to afford a heterobimetallic Zn/Mg alkyl-carbamato derivative [213].…”

Cooperative Bond Activation and Facile Intramolecular Aryl Transfer of Nickel–Aluminum Pincer‐type Complexes

“…Similar aryl group migrations have been previously observed in Rh and Ir complexes in the PBP ligand frameworks, [9a,24] as well as for (PSiP)Ni complexes. [25] This reaction has been described as an overall oxidative insertion of aT Mc enter into an LA À Cb ond. [24] In the specific case presented here,t his is ar elatively facile conversion of a s-accepting alane in 2 into an aluminyl ligand in 8-THF that is induced by the addition of THF.P reviously,t he syntheses of TM-aluminyl complexes required harsh reductants, [9b, 10g] preformation of an Al I precursor, [10e,h] or salt metathesis.…”

Metal complexes containing silicon‐based pincer ligands: Reactivity and application in small molecule activation

“…In accordance with the results of kinetic studies, two different reaction pathways for the generation of the carbamato species were proposed, specifically a reductive elimination followed by oxidative addition and normal CO 2 insertion for nickel amido species, and a concerted mechanism probably via metal-ligand cooperation of the nickel phenyl species (Scheme 8). 144 For CO 2 activation, the utilization of a silicon donor as ligand is advantageous because silicon cooperatively binds carbon dioxide along with a metal ion. After coordination, silicon-bound CO 2 may be converted to CO owing to the high affinity of silicon for bonding with oxygen.…”

“…Lee and co‐workers reported the CO 2 reaction of [(RSiP i Pr 2 )Ni] complexes to generate the nickel(II) carbamato species [(RSiP i Pr 2 )Ni II (OCONHAr)] (R = Me, Ph; Ar = mesityl or 2,4,6‐triisopropylphenyl) 143,144 . It is worth noting that the silyl moiety acted along with the nickel center as the reactive site during the reaction with CO 2 .…”