Naphthyl hydride complex

Perutz and coworkers [180] have used 2D EXSY to study the dynamic behavior of RhCp(PMe3)(q -naphthalene), 109, which is thought to be a model intermediate for the oxidative addition of arenes to a metal center. In this complex, there are two processes taking place. The first involves an equilibrium between the -naphthalene complex, 109, and the naphthyl hydride complex, 110. The second process involves an intramolecular [l,3]-shift which moves the coordination site of the naphthalene ring from one side of the ring to the other (Scheme 1.12). 

Chatt and Davidson, in combination with subsequent work by Cotton et al., demonstrated that Ru with two bisphosphine ligands, RuOv -F.F-MejPCHjCHjPMejH, reacts to break a phosphine methyl C H bond to give a dimeric Ru(II) cyclometalated product (Equation 11.1).18 In addition, the combination of Ru(fc2-P,P-Me2PCH2CH2PMe2)2 with naphthalene provides the Ru(II) naphthyl hydride complex.19 These reactions were among the first examples of well-defined metal-mediated C H bond cleavage. 

Intermolecular oxidative addition of H—C usually involves activated H—C bonds. The weak acid HCN reacts with transition-metal complexes e.g., HCN and NiL lead to the hydride complexes HNi(CN)Lj (L = various phosphorus ligands). The versatile complex IrCl(CO)(PPh3)j adds HCN cleanly in CH Clj at RT to form HIr(CN)(Cl(PPhj)2. The zero-valent complexes Pt(PPhj) or Pt(PPh3)3 also add HCN to yield HPt(CN)(PPh3)j. Reactions of HMNp(dmpe)j (M = Fe, Ru, Os Np = 2-naphthyl dmpe = Me PCH CH PMej) with HCN and terminal acetylenes give HMR(dmpe)2 that contain new M—C bonds (R = — CN, — CjR ) . 

Reactivity from the naphthyl hydride ruthenium complex is believed to occur via initial reductive elimination of naphthalene followed by oxidative addition of a C-H bond. These activation processes (requiring reductive elimination) occur at temperatures of 150°C in alkane or arene solvents, depending on the desired product ". This complex shows general C-H activation behavior with sp, sp, and sp hybridized C-H bonds . ... 

IV,A,2a) has an interesting comparison in the behavior of the complex Ru(naphthalene)(PP)2 (VII). Spectroscopic evidence has shown that in solution this complex is in equilibrium with the 2-naphthyl hydride (VIII) (34). 

The second Heck reaction involves a naphthyl iodide (Ar2 = 2-naphthyl) but the initial mechanism is much the same. However, the enol ether has two diastereotopic faces syn or anti to the aromatic substituent (Ar1) introduced in the first step. Palladium is very sensitive to steric effects and generally forms less hindered complexes where possible. Thus coordination of the palladium(II) intermediate occurs on the face of the enol ether anti to Ar1. This in turn controls all the subsequent steps, which must be syn, leading to the trans product. The requirement for syn p-hydride elimination also explains the regiochemical preference of the elimination. In this cyclic structure there is only one hydrogen (green) that is syn the one on the carbon bearing the naphthyl substituent is anti to the palladium and cannot be eliminated.. ... 

The complexes Na + RSi(-C6H46)2 (R = Me, Ph, 1 -Naphthyl) were also found130 to be very reactive towards nucleophilic reagents such as organometallic reagents and hydrides. An excess of hydride leads to trihydrogenosilanes (equation 13). 

High diastereofacialselectivity (90-98%) was similarly achieved in the reduction of the related imine complexes (110 R = H or Me, Ar = Ph or Z-naphthyl) with NaBH4 or NaBD4 in methanol. The stereochemical outcome of these reductions can be explained by attack of hydride on the conformer (111) in which allylic 1,3-strain is minimized. Stereoselectivity was... 

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