Hydride cyclometalated

CpReL3 (L = PMe3) is also photoreactive with alkanes by loss of The product is CpReL2(R)H (R = methyl, 1-hexyl, cyclopentyl and cyclopropyl). The more sterically hindered substrate, cyclohexane, did not give an alkyl hydride cyclometalation of the coordinated PMe3 or oxidative addition of the C—H bond of the free L takes place instead. This more bulky system has a lower tolerance for steric bulk in the alkane. 

Reaction of the cyclometallated complexes 244-246 with pyrazole and excess sodium hydride affords cyclic dimers 247 (990M3991), where C N denotes the corresponding cyclometallated ligand in accordance with structures 244-246. The [Pt2(thienylpyridine)2(/j.-pz)](C104)3] is known as well. 

Treatment of [IrCl(CO)2(/ -toluidene)] with azine phosphines of type Z, -PPh2CH2C( Bu) =N-N=C(Q)R, Q = H, Me, R = an organic group, activates aryl, heterocyclic, alkenyl, or aliphatic C—H bonds to give cyclometalated Ir111 hydrides.339... 

Crabtree and coworkers used the cyclometallated lr(lll)-hydride complex 19 for the intramolecular hydroalkoxylahon and hydroaminahon of aromatic alkynes (Equahon 6.10) [25], while Liu and coworkers used the neutral lr(lll)-hydride complex 20 in combinahon with cocatalytic amounts of NaB[3,5-C6H3(CF3)2]4 for the synthesis of a range of indoles (Table 6.4) [26]. 

Mdssbauer spectra of bonding and structure in, 15 184-187 reactions with diborane, 16 213 stabilization of, 5 17, 18-19 cyanates, 17 297, 298 cyanide complexes of, 8 143-144 cyclometallated bipyridine complex, 30 76 diazene complexes, 27 231-232 dinitrogen complexes, 27 215, 217 diphosphine complexes of, 14 208-219 dithiocarbamates, 23 253-254 -1,2-dithiolene complexes, 22 323-327 hydrogen bonding, 22 327 halide complexes with phosphine, etc., 6 25 hexaflouride, structure, 27 104 hydride complexes, 20 235, 248-281, see also Transition metal-hydride complexes... 

RhHClIBu CH HgCHCHaCH BuJ ], and a small amount of an olefinic diphosphine-rhodium(I) complex (vide infra). The 16-atom chelate exists in solution as predominantly one rotamer, with about 10% of a second rotamer (P-31 and H-l NMR evidence) (34). The probable structures of these two rotamers are Complexes IX and X or vice versa. The cyclometallated hydride complex [ithHClIBu CI CH2CHCH2CI12PBU2 ] has the configuration of Structure XI by X-ray... 

We find that on treating the 16-atom ring binuclear dihydride tetrachloride complex with a base such as 2-methylpyridine to remove the elements of hydrogen chloride from the rhodium, smooth conversion to the cyclometallated hydride complex occurs. A possible sequence of reactions leading to this overall conversion is shown in Scheme I. 

The H-l NMR spectrum of the cyclometallated hydride (Structure XI) shows no hydride resonance at room temperature, but on cooling a broad resonance starts to appear, and at -62°C it shows resolved coupling to 31P (19 Hz) and 103Rh (55 Hz). We ascribe this temperature-dependent behavior to the occurrence of a rapid, reversible C-H/Rh-H fission such as shown in Scheme II. Alternatively there may be rapid, reversible oxidative additions, Structure XII Structure XI, as in Scheme I. 

Hydride donors, such as LiAUTi or NaBH4, will cleave Pd bonds, including those in cyclometalated complexes. If the molecule contains groups that will react with hydride reagents, the same transformation can be carried ont nsing H2 (eqnation 79). This reaction has been nsed with LiAlD4 to establish the precise position of metalation. 

In another example, the cyclometalated iridium complex [Ir(ppy)2(4-vinylpyridine)Cl] has been attached via hydrosilation see Hydrosilation) to hydride-terminated poly(dimethylsiloxane) to produce a luminescent material. Evaluation of this material as a luminescent oxygen sensor revealed significantly improved sensitivity over dispersions of the original vinyl pyridine complex in poly(dimethylsiloxane). The luminescent material was blended with polystyrene to give a new sensor that exhibited increased sensitivity and maintained short response times to rapid changes in air pressure. 

Major achievements in cyclometallation processes involving NHC ligands have been achieved by Nolan and coworkers. It was observed that the solvent could play a crucial role in the formation of rhodium- and iridium-based complexes. As shown in Scheme 39, the reaction performed in pentane between [M(COE)2Cl]2 (M = Rh or Ir) and four equivalents of FBu led only to COE substitution by the NHC ligand affording rhodium-based product (243) (the iridium complexing proving difficult to isolate). On the other hand, the same reaction carried out in hexanes gave, via C H activation, the hydride complexes (244) and (245). Finally, in benzene, a unique double cyclometallation process occurred to yield the coordinatively unsaturated 16-electron... 

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