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Cationic rhenium dihydrogen complexes, [Re(H2)(PR3)2(CO)3]B(Ar‘)4 (PR3 = PCy3, PiPr3, PiPrPh2, PPh3; Ar‘ = 3,5-(CF3)2C6H3), have been prepared by the protonation of ReX(PR3)2(CO)3 (X = H, CH3) with [H(Et2O)2]B(Ar‘)4 under a hydrogen atmosphere. Deuterium is incorporated into the H2 ligand when placed under a D2 atmosphere and large J HD values (30−33 Hz) are consistent with a dihydrogen formulation. Relaxation data indicate very short T 1min for these complexes. These complexes are susceptible to heterolytic cleavage of dihydrogen, and the reactivity with several bases has been investigated. Under vacuum or argon atmosphere the complexes readily lose hydrogen to form 16-electron complexes. In the solid state, [Re(PCy3)2(CO)3]B(Ar‘)4 exhibits an agostic interaction to a β C−H bond of the phosphine ligand. Variable-temperature 31P{1H} NMR spectra of [Re(PCy3)2(CO)3]B(Ar‘)4 indicate a dynamic process involving hindered rotation about the Re−P bond. Competition studies have been conducted, and the hydrogen binding affinity is higher for [Re(H2)(PCy3)2(CNtBu)3]B(Ar‘)4 (5) than for [Re(H2)(PCy3)2(CO)3]B(Ar‘)4 (2a). Similar experiments also find that 5 also binds hydrogen preferentially over W(H2)(PCy3)2(CO)3.

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Reaction of Cp2ReCH2R (R = H, CH3) (Cp = η5-C5H5) with [Ph3C]B(Ar‘)4 (Ar‘ = 3,5-CF3)2C6H3) generates carbene complexes [Cp2ReCH2]B(Ar‘)4 (1) and [Cp2ReCH(CH3)]B(Ar‘)4 (3). Complex 1 is thermally robust and is only observed to decompose to [Cp2Re(C2H4)]+ and [Cp2Re(NCCD3)]+ upon prolonged thermolysis in acetonitrile-d 3 or upon addition of BF4 - or PF6 - salts. The formation of 1 is also observed upon reaction of [Cp2Re(CH3)H]B(Ar‘)4 with CH2Cl2 at 0 °C to give [Cp2Re(CH2Cl)Cl]B(Ar‘)4 (2) followed by treatment with Mg. The electrophilic nature of 1 is confirmed by adduct formation with PPh3, pyridine, and CNtBu. Complex 1 reacts with halogens by 1,2-addition across the Re−C double bond to form halomethyl halide complexes [Cp2Re(CH2X)X]B(Ar‘)4 (X = Cl, Br, I). Reaction of 1 with pyridine N-oxide gives the formaldehyde complex [Cp2Re(η2-H2CO)]B(Ar‘)4. The formaldehyde ligand can be displaced in solution by reaction with PPh3, acetonitrile, or methylene chloride. Complex 1 reacts with sulfur-atom donor reagents to give the thioformaldehyde complex [Cp2Re(η2-H2CS)]B(Ar‘)4. Reaction of 1 with N2CHSiMe3 generates the olefin complex [Cp2Re(η2-H2CCHSiMe3)]B(Ar‘)4.

Complexes of rhenocene (Cp2Re) with substitution at the cyclopentadienyl rings have been prepared from Cp2Re−Me by dilithitation of the Cp rings followed by reaction with Me2SiCl2 or Cl(SiMe2)2Cl to afford ansa-bridged species. Protonation of the resulting neutral Re methyl complexes gives thermally labile methyl hydride complexes. The thermal stability of the methyl hydride complex with a single silicon atom in the ansa bridge is enhanced with respect to the unbridged analogues.

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