Solid-State 65Cu and 31P NMR Spectroscopy of Bis(triphenylphosphine) Copper Species
Bryan E. G. Lucier†, Joel A. Tang†, Robert W. Schurko*†, Graham A. Bowmaker‡, Peter C. Healy§ and John V. Hanna*
J. Phys. Chem. C, 2010, 114 (17), pp 7949–7962
Abstract: Frequency-stepped ultrawideline (UW) 65Cu solid-state NMR (SSNMR) experiments have been performed on a series of nine bis(triphenylphosphine) copper(I) species, with eight of these having an oxyanion-based ligand and one a borohydride ligand. These copper atoms reside in spherically asymmetric environments featuring two covalent Cu−P bonds and coordination from single bidentate ligands. The QCPMG pulse sequence was utilized in NMR experiments on all of the samples, along with the WURST-QCPMG sequence on select samples, to acquire UWNMR spectra of high quality. In all cases, large 65Cu quadrupolar coupling constants (CQ) between 40.8 and 51.7 MHz are observed, and are confirmed by NQR measurements. The immense quadrupolar interactions and their correspondingly large contributions to the central-transition powder patterns make accurate quantification of copper chemical shift anisotropy (CSA) difficult, though CSA effects are observed. 1H−31P CP/MAS NMR spectra reveal one-bond J-couplings, 1J(65/63Cu, 31P), for all complexes, as well as the presence of residual dipolar coupling, which enables determinations of both the sign of CQ and the orientation of the EFG tensor with respect to the Cu−P dipolar vector (both of which are unavailable from standard 65Cu SSNMR experiments). The 65Cu EFG parameters and 1J(65/63Cu, 31P) coupling constants are sensitive to the local geometry and bond lengths about the Cu center. Ab initio calculations are used to confirm experimentally predicted orientations of the Cu EFG tensors, to predict experimental CQ, ηQ, and CS tensor values, and to aid in identifying relationships between the copper NMR parameters and molecular structures. This combination of experimental and theoretical NMR data enables the correlation of symmetry and local structure with copper NMR parameters, further extending the applicability of copper SSNMR spectroscopy to a wide variety of copper-containing systems.