† Electronic supplementary information (ESI) available: GC-MS analysis, digital camera images of freeze-dried CNCs, EDAX analysis of PdNPs@CNCs nano-composite, histogram for Pd nanoparticles from TEM picture and FTIR spectra of CNCs before and after deposition of Pd nanoparticles, XPS spectra of Pd3d in PdNPs@CNCs, TGA spectra of CNCs under nitrogen and air atmosphere. See

The compound Cp(2)TiMe(2) reacts with [Ph(3)C][B(C(6)F(5))(4)] in CD(2)Cl(2) at 205 K to give, inter alia, [Cp(2)TiMe(CD(2)Cl(2))][B(C(6)F(5))(4)]. This solvent-separated ion pair reacts in turn with 2,4-dimethyl-1-pentene (DMP) to give a series of cationic species, the first being the alkene complex [Cp(2)TiMe(DMP)](+), which undergoes ready migratory insertion to form the σ-alkyl complex [Cp(2)Ti(CH(2)CMe(2)CH(2)CHMe(2))](+). The latter, which does not contain a β-hydrogen atom, rearranges rapidly via an unprecedented 1,5-σ bond metathesis reaction involving two isomeric ε-agostic species to give the σ-alkyl species [Cp(2)Ti(CH(2)CHMeCH(2)CMe(3))](+); this does contain a β-hydrogen atom and, in concurrent processes, eliminates H(2) or 2,4,4-trimethyl-1-pentene (a major product) to form respectively the allylic complex [Cp(2)Ti{η(3)-(CH(2))(2)CCH(2)CMe(3)}](+) (a major product) or the hydride complex [Cp(2)TiH](+). The latter reacts reversibly with free DMP to give the insertion product [Cp(2)Ti(CH(2)CHMeCH(2)CHMe(2))](+) (V, a major product), in which the italicized hydrogen atom engages in a β-agostic interaction with the metal atom. Compound V is a rare example of both a β-agostic derivative of a group 4 metallocene and a β-agostic compound of any metal in which the (1)H resonance of the agostic hydrogen can be identified in the (1)H NMR spectrum (δ -3.43). Interestingly, a NOESY experiment on V indicates slow mutual exchange between the agostic hydrogen atom, the hydrogen atoms on C(1), and those of Me(2). These observations are consistent with the intermediacy of the allylic dihydrogen species [Cp(2)Ti(H(2)){η(3)-(CH(2))(2)CCH(2)CHMe(2)}](+), which loses H(2) to form [Cp(2)Ti{η(3)-(CH(2))(2)CCH(2)CHMe(2)}](+) (a minor product). Support for all steps of the proposed reaction scheme comes from product distributions, from labeling studies utilizing [Cp(2)Ti(CD(3))(CD(2)Cl(2))](+), and from extensive DFT calculations. The observed titanocene-based chemistry stands in stark contrast to that of the analogous zirconium system, in which the unusual but well-characterized cationic methyl alkene complex [Cp(2)ZrMe(DMP)](+) does not undergo migratory insertion and subsequent reactions.

The compound [Cp2Ti(Me)(CD2Cl2)][B(C6F5)4] reacts with trimethylvinylsilane (TMVS) to form the 1,2-insertion product [Cp2TiCH2CHMe(SiMe3)](+) (III), which exists in solution as equilibrating β- and γ-agostic isomers. In addition, while free rotation of the β-methyl group results in a single, averaged γ-H atom resonance at higher temperatures, decoalescence occurs below ~200 K, and the resonance of the γ-agostic hydrogen atom at δ ~ -7.4 is observed. Reaction of [Cp2Ti(CD3)(CD2Cl2)](+) with TMVS results in the formation of [Cp2TiCH2CH(CD3)(SiMe3)](+), which converts, via reversible β-elimination, to an equilibrium mixture of specifically [Cp2TiCH2CH(CD3)(SiMe3)](+) and [Cp2TiCD2CD(CH3)(SiMe3)](+). Complementing this conventional process, exchange spectroscopy experiments show that the β-H atom of [Cp2TiCH2CHMe(SiMe3)](+) undergoes exchange with the three hydrogen atoms of the β-methyl group (β-H/γ-H exchange) but not with the two α-H atoms. This exchange process is completely shut down when [Cp2TiCH2CH(CD3)(SiMe3)](+) is used, suggesting an H/D kinetic isotope effect much larger (apparently >16,000) than the maximum possible for an over-the-barrier process. It is proposed that β-H/γ-H exchange is facilitated by quantum mechanical proton tunnelling in which a hydrogen atom of the 2-methyl group of the alkene-hydride deinsertion product [Cp2TiH{CH2═CMe(SiMe3)}](+) undergoes reversible exchange with the hydride ligand via the allyl dihydrogen species [Cp2TiH2{(η(3)-CH2C(SiMe3)CH2}](+). Complementing these findings, DFT calculations were carried out to obtain energies and NMR parameters for all relevant species and thence to obtain better insight into the agostic preference(s) of complex III and the observed exchange processes. In all cases where comparisons between experimental and calculated data were possible, agreement was excellent.

Reaction of [Cp2Ti(Me)(CD2Cl2)]+ (I) with 3,3-dimethyl-1-butene in CD2Cl2 at 205 K produces the α-agostic insertion product [Cp2TiCH2CHMetBu]+ (II), in which the chirality at C(2) induces preferential agostic binding of one of the diastereotopic α-H atoms; subsequent coordination of ethyl ether to II leaves the α-agostic interaction weakened but intact. On warming, II undergoes β-hydrogen elimination and the resulting hydride reacts further with excess 3,3-dimethyl-1-butene to form the β-agostic species [Cp2TiCH2CH2tBu]+. NMR data and calculated (DFT) energies support the assignments