Insertion of Isonitriles into the Zr–CH₃ Bond of Cp*₂Zr(CH₃)₂ and Electrophilic Cleavage of the Remaining Methyl Group

Abstract

The insertion of tert-butyl isonitrile ( t BuNC) into the M−C bond of Cp* 2 Zr(CH 3 ) 2 (1) leads to the formation of a monoiminoacyl product Cp* 2 Zr(iminoacyl)CH 3 (2). SC-XRD analysis has revealed that the η 2 coordinated iminoacyl ligand has an "N-outside" orientation. Compound 2 undergoes rapid Zr−C bond cleavage with the Brønsted acid CpCr(CO) 3 H or the Lewis acid B(C 6 F 5 ) 3 , yielding Zr cation 4 or 5 with the corresponding anion [MeB(C 6 F 5 ) 3 ] − or [CpCo(CO) 3 ] − . In the solid-state structure of 4, the Zr cation features an η 2 "N-inside" geometry for the iminoacyl group and interacts with the [CpCo(CO) 3 ] − via the oxygen atom of one of the CO ligands. Cleavage of the methyl ligand from the Zr of 1 with CpCr(CO) 3 H proceeds with a second-order rate constant k 1 of 2.11(4) × 10 −3 M −1 s −1 , whereas cleavage of the methyl ligand from the Zr of 2 is significantly faster, with an estimated k 2 greater than 10 4 M −1 s −1 . In light of the observed "N-outside" to "N-inside" change from 2 to 4, we propose that the enhanced rate with 2 is due to initial protonation of its nitrogen, subsequent outside-toinside rotation, and eventual transfer of the proton onto the Zr−C bond.

Linearly Bridging N2 versus CO: Chemical Bonding and Spin‐Controlled Reactivity.

“…IR bands at 1792 cm −1 and 1895 cm −1 are assigned to the asymmetric and symmetric stretching vibrations of the terminal CO ligands, while the band at 1542 cm −1 is in the typical range of bridging isocarbonyl (Figure 3, bottom left) [30–33] . The bathochromic shift confirms significant charge transfer and predominant C−O double bond character, which is in agreement with the structural parameters.…”

“…IR bands at 1792 cm À 1 and 1895 cm À 1 are assigned to the asymmetric and symmetric stretching vibrations of the terminal CO ligands, while the band at 1542 cm À 1 is in the typical range of bridging isocarbonyl (Figure 3, bottom left). [30][31][32][33] The bathochromic shift confirms significant charge transfer and predominant CÀ O double bond character, which is in agreement with the structural parameters. Magnetic characterization of 6 by SQUID magnetometry reveals a constant magnetic moment (χ M T = 3.46 cm 3 • K • mol À 1 ) in the temperature range 10-210 K, which can be fitted with a S = 2 spin state (spin-only value of 3.00 cm 3 • K • mol À 1 ) assuming a single d 4 high-spin ion (Figure 3, top left).…”

Structural Diversity in the Reactions of Dimetallic Alkyl Titanium Oxides with Isonitriles and Nitriles

“…In addition to the plausible formation of the isomers analyzed in Schemes and , the rotation of the iminoacyl ligands lead to different isomers ( endo – exo ) as described in Scheme for compounds anti - 4a (R′ = Me) and anti - 3a (R′ = t Bu) and as previously reported for other η 2 -iminoacyl complexes. ,− …”

Synthesis, Characterization, and Catalytic Activity of Bimetallic Ti/Cr Complexes

“…We have obtained a variety of Zr/M (M = Cr, Mo, and W) bimetallic complexes by the reaction of Cp 2 Zr­(R)­CH 3 (R = methyl, acyl, or iminoacyl) with acidic metal hydrides. The rate of cleavage of the Zr–CH 3 bond depends on the nature of the adjacent R, and is significantly enhanced when R can act as a proton relay site. − …”