V-Heterocyclic carbene complexes

V-Heterocyclic Carbene Complexes in Arylation Reactions other than Cross-couplings... 

The novel catalyst system based on palladium(O) /V-heterocyclic carbene complexes was developed by the group of Beller, in part prompted by the strong patent position of Dow on phosphine-based palladium catalysts [8]. The catalyst [37], either generated in situ from the corresponding imidazolium salt or the molecularly defined divinyldisiloxane complex [Pd(Imes)(dvds)] (Fig. 3), was used in the telomerization of 1,3-butadiene with methanol [38—40]. The /V-heterocyclic carbenes are in general better a-donor ligands and come with considerably different steric requirements than the phosphines. The [Pd(Imes)(dvds)] complex resembles the final telomer-palladium product complex and thus offers a facile and clean entry into the catalytic cycle. The metal carbene complex was shown to be... 

Chapter 10 in the first edition covered metal carbene complexes, metathesis, and polymerization reactions. The chapter has now been split into two chapters. Chapter 10 now emphasizes the chemistry of carbene complexes new material on /V-heterocyclic carbene complexes, with applications in synthesis, has been introduced. Chapter 11 now considers metathesis and polymerization. The sections on the discovery and elucidation of n-bond metathesis have been rewritten and expanded. The discussion of both metathesis and Ziegler-Natta polymerization reactions has been considerably enhanced and brought up to date. 

CYCLOPENTADIENYL-FUNCTIONALIZED (V-HETEROCYCLIC CARBENE COMPLEXES OF IRON AND NICKEL... 

Dam JH, Osztrovszky G, Nordstrpm LU, Madsen R (2010) Amide synthesis from alcohols and amines catalyzed by ruthenium V-heterocyclic carbene complexes. Chem Eur J 16 6820... 

Extensive mechanistic studies have been conducted on the oxidative addition of aryl halides to Pd(0) complexes ligated by PPh3 in different media and with different additives175, 176. However, palladium complexes containing these ligands are not active catalysts for amination. Instead, one must consider the addition of aryl halides to palladium complexes bound by ligands relevant to amination. Studies of the mechanism of oxidative addition to palladium(O) complexes of P(tol-o)3, DPPF, BINAP, Q-phos, P(Bu-f)3 and an /V-heterocyclic carbene ligand have been reported. 

Catalysts derived from /V-heterocyclic carbenes have also been demonstrated as highly effective catalysts for hydrovinylations involving heterocoupling of aromatic and aliphatic alkenes (Scheme 3-93). In this case, the catalyst is prepared by coupling an aldehyde and aliphatic alkene with a Ni(0) NHC complex in the presence of a silyl triflate. 

Olefin metathesis reaction that reorganizes carbon-carbon double bonds provides fundamentally new strategies for natural product synthesis and polymer chemistry. Hilvert and coworkers built up an artificial metalloenzyme by covalently tethering a Grubbs-Hoveyda-type Ru complex to a protein scaffold [78]. An /V-heterocyclic carbene (NHC) ligand, which has been reported as a suitable ligand for a number of water-soluble ruthenium-based metathesis catalysts, was derivatized with an electrophilic bromoacetamide. The Ru carbene complex (27 in Figure 10.16) was then attached by site-selective alkylation of the cysteine... 

An exactly opposite trend was observed in olefin metathesis for which the mechanistic scheme for complexes 4 and 5 postulates the dissociation of a phosphine ligand from the metal centre as the key step in the dominant reaction pathway [23]. For instance, ruthenium benzylidene complexes 5 bearing only one /V-heterocyclic carbene entity were found to be significantly more active than those incorporating two of them (6) and the original Grubbs complex (4). This was clearly substantiated for the conversion of the suitable dienes into dihydropyrrole (Scheme 6, Table 2) [20d], and polyhydroxylated cyclohexene rings [24]. 

Oxidative addition is still one of the key processes observed in the literature. In fact, a better understanding of the steric and electronic properties of complexes that can promote C—H bond activation throughout this mechanism has been widely studied. The recent work of Conejero and coworkers [13] highlights this interest by the alteration of the environment of the V-heterocyclic carbene (NHC) ligands on a series of stable T-shaped [Pt(NHC )(NHC)][BAFj, where NHC represents the cyclometallated ligand, species (Fig. 25.6). 

Z. S. Qureshi, S. A. Revankar, M. V. Khedkar, B. M. Bhanage, Catal. Today 2012,198,148-153. Aminocarbonylation of aryl iodides with primary and secondary amines in aqueous medium using polymer supported palladium N-heterocyclic carbene complex as an efficient and heterogeneous recyclable catalyst. 

Complex 21 bearing a four-membered /V-heterocyclic carbene was reported by Grubbs et al. [35] (Scheme 14). However, its catalytic activity was found to be quite lower than that of catalysts 3 and 6. 

Very recently [54] a 2e reductirMi of V-heterocyclic carbene-carbonyl Mn(I) to Mn(—I) has been reported which occurs at the same potential (—1.35 V vs SCTE) instead of two consecutive potentials separated by a few hundred mV as shown for analogous MnBr(CO) t(2N 1). Such Mn complexes catalyse very selectively the CO2 to CO reduction with a faradaic efficiency of 34.6 %. 

Ru-catalyzed AROM/CM sequences served as a key step in the total synthesis of baconipyrone C (163, Scheme 24.42), a marine polyketide isolated from Siphonaria baconi The employed Ru carbene [Ru]-VI is generated in situ by treatment of the achiral Ru-PCya complex with Ag-based V-heterocyclic carbene (NHC) and Nal. And then, the [Ru]-VI-catalyzed AROM/RCM of oxabicycle 161 with styrene (8 equiv) afforded the fully substituted pyran 162 in 62% yield and in 88% ee. The additional transformations led to 163 in good overall yield. Although this application of AROM/CM process to 161 was the first and rare example of Ru-catalyzed enantioselective olefin metathesis process, very recently, an application of enantioselective RCM reaction catalyzed by [Ru]-VII to the synthesis of (—)-5-e/>/-citreoviral has been reported by Funk. ... 

Synthesis and structural characterization of linear Au(I) N-heterocyclic carbene complexes New analogs of the Au(I) phosphine drug Auranofin, M. V. Baker, P. J. Barnard, S. J. Berners-Price, et al., J. Organomet. Chem., 2005, 690, 5625. 

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