<sup>13</sup>C<sub>carbene</sub> nuclear magnetic resonance chemical shift analysis confirms Ce<sup>IV</sup>C double bonding in cerium(<scp>iv</scp>)–diphosphonioalkylidene complexes
C. Baker, John A. Seed, Ralph W. Adams, Daniel Lee, Stephen T. Liddle
Abstract
C chemical shift tensor spans of any alkylidene complex to date (1, 801 ppm; 2, 810 ppm). In contrast, the phosphonium-substituent shielding contributions are much smaller than the Ce[double bond, length as m-dash]C σ- and π-bond components. This study confirms significant Ce 4f-orbital contributions to the Ce[double bond, length as m-dash]C bonding, provides further support for a previously proposed inverse-trans-influence in 2, and reveals variance in the 4f spin-orbit contributions that relate to the alkylidene hybridisation. This work thus confirms the metal-carbon double bond credentials of f-element-diphosphonioalkylidenes, providing quantified benchmarks for understanding diphosphonioalkylidene bonding generally.