Nitrous oxide (N 2 O) and organoazides (N 3 R′) are energy-rich molecules that undergo a variety of reactions with group 10 transition metal complexes resulting in transfer of an "O" or "NR" moiety to the metal with loss of dinitrogen. Complexes of the type L 2 NiR 2 (L ) PMe 3 ; L 2 ) bipyridine, phenanthroline; R ) alkyl, aryl) undergo quite general insertion reactions with nitrous oxide to afford alkoxide or aryloxide products L 2 NiR(OR) 1 and with organoazides to yield amide derivatives L 2 NiR(NR′R) upon N 2 extrusion. 2 Organoazides have also been shown to react directly with unsaturated group 10 metal fragments to give imido complexes like (Ph 2 MeP) 2 MdNCF 2 CFHCF 3 (M ) Pd, Pt), 3 [Me 2 C 3 H{(2,6-Me 2 C 6 H 3 )N} 2 ]NidNAd, 4 and (dtbpe)NidNMes (dtbpe ) 1,2-bis(di-tert-butylphosphino)ethane). 5 In the course of investigating group-transfer reactions of ligands involved in multiple-bonding to three-coordinate nickel, 6 we encountered facile reactions of nitrous oxide and organoazides with Ni-carbene and -imido complexes that generate new CdN, CdO, and NdN double bonds. Herein we report the results of these studies, including experimental and computational data that give insight into the mechanism of these unusual heteroatom-coupling reactions.Reaction of cold diethylether solutions of the green diphenylcarbene complex (dtbpe)NidCPh 2 (1) 7 with 2 equiv of mesitylazide (N 3 Mes) or 1-adamantylazide (N 3 Ad) results in elimination of N 2 and formal "carbene-nitrene" coupling to give the corresponding ketimines RNdCPh 2 (2a, R ) Mes; 2b, R ) Ad) in 76% and 72% isolated yields, respectively (Scheme 1). The resulting "(dtbpe)Ni 0 " fragment is trapped by a second equivalent of N 3 R to give the known organoazide complexes (dtbpe)Ni(η 2 -N 3 R) (3a, R ) Mes; 3b, R ) Ad) as kinetic products that undergo subsequent thermal N 2 elimination to afford the Ni(II) imido complexes (dtbpe)NidNR (4a, R ) Mes; 4b, R ) Ad) as the ultimate nickel-containing products. 5 Such transition metal mediated carbene-nitrene coupling reactions are unusual, but not unprecedented. Fischer has shown that (CO) 5 MdCPh 2 reacts with N 3 R to give (CO) 5 M(κ 1 -NRdCPh 2 ) (M ) Cr, W), 8 and Grubbs has reported that N 3 R reacts with (N(2-P-i-Pr 2 -4-Me-C 6 H 3 ) 2 )IrdCH(O-t-Bu) to afford RNdCH(O-t-Bu) and (N(2-P-i-Pr 2 -4-Me-C 6 H 3 ) 2 )Ir(N 2 ). 9 A novel intramolecular imido-carbene coupling reaction has been observed by Meyer in a (trisNHC)CodNR complex (NHC ) N-heterocyclic carbene). 10 A kinetic study of the reaction of 1 with N 3 Ad was carried out to gain mechanistic insight into ketimine (2b) formation. (The reaction of N 3 Mes with 1 was too fast to conveniently be monitored by NMR, even at low temperature.) Disappearance of 1 and formation of 2b were followed by 1 H NMR spectroscopy over a temperature range of 35-65°C (C 7 D 8 solution). The reaction is first-order in both [1] and [N 3 Ad] with a second-order rate constant of 1.7 × 10 -3 ((0.2) M -1 s -1 at 35°C. No intermediates were observed when the reaction was foll...
The synthesis and redox reactivity of unusual bent nickel-arylimido complexes of the type L 2 Ni]NAr supported by a new chelating bis(N-heterocyclic carbene) ligand are described, including experimental, structural, and computational data to validate this atypical binding motif. Upon oxidation the strongly bent imido complex undergoes C,C-coupling and dehydrogenation to afford a complex bearing an unusual diphenoquinonediimine ligand bridging two Ni(II) centers.
Chromium(III) tetraphenylporphyrin chloride, TPPCrCl, in the presence of bis(triphenylphosphine)iminium chloride, PPN + Cl − , is shown to react catalytically with styrene oxide, SO, under various conditions to lead to poly(styrene oxide), PSO, poly(styrene carbonate), PSC, styrene carbonate, SC, poly(styrene succinate), PSS, and β-hydroxyester. The stereochemical consequences of the ring-opening event in this coordination catalysis have been investigated by NMR spectroscopy, polarimetry, and chiral HPLC, employing both racand R-SO. The ring-opening event occurs by attack at both the methylene and methine carbons and nucleophilic attack at the methine occurs preferentially with inversion. These findings concerning coordinate catalysis are compared with the more common ring-opening reactions in organic chemistry and the recent report on the cobalt-catalyzed formation of PSC by Darensbourg and co-workers.
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