Effect of ring size on NMR parameters: cyclic bisphosphine complexes of molybdenum, tungsten, and platinum. Bond angle dependence of metal shieldings, metal-phosphorus coupling constants, and the phosphorus-31 chemical shift anisotropy in the solid state

Aspects of equivalence as illustrated by phosphine complexes of transition metals

“…The 31 P CP/MAS spectra of the cis-(DBP) 2 M(CO) 4 series indicate two inequivalent DBP ligands, which in the case of cis-(DBP) 2 Cr(CO) 4 has been verified by X-ray crystallography (54). In contrast to the insensitivity of 33 , the two other principal components of the phosphorus chemical shift tensor change in a characteristic and almost constant manner to lower frequencies on descending the group, viz., by 17-32 ppm from Cr to Mo and by 25-37 ppm from Mo to W. Such effects have been observed previously in 31 P NMR spectra of molybdenum and tungsten phosphine complexes (53,58) and are analogous to changes in carbon chemical shift tensors of the hexacarbonyls (63). Clearly, variations in 11 pendicular to the M-P bond (i.e., 11 and 22 ) to the nature of the metal is not unexpected.…”

“…Thus, for example, whereas both (dppm)Mo(CO) 4 and (dppe)Mo(CO) 4 exhibit two chemical shifts in Figure 9 The effects of 1 H decoupling and magic angle spinning (MAS) on the appearance of the solid-state 31 their CP/MAS 31 P NMR spectra, (dppp)Mo(CO) 4 exhibits only one (25).…”

“…The isotropic chemical shifts follow the trends known from many 31 P NMR solution studies; viz., as one descends within the same group, the phosphorus nucleus becomes more shielded (56). On average, there is an increase in the shielding of 20 ppm between Cr and Mo and between Mo and W. The orientation of phosphorus CS tensors in metal phosphine complexes has been determined experimentally for only a few complexes of molybdenum (18), platinum (57,58), rhodium (59), mercury (60), indium (61), and manganese (62), using either single-crystal or dipolar-chemical shift techniques. In many of these complexes, the principal component with chemical shifts of −20 to −40 ppm roughly corresponds to the direction of the M-P bond; in many (but not all!)…”

A simple molecule with a complex crystal structure: interplay of 31P solid‐state NMR spectroscopy and single‐crystal x‐ray diffraction in the structure determination of a ruthenium diphosphine diamine complex

“…Because the results 27 This similarity is mainly based on the values of υ 33 ; for most complexes they are in the range 30 to 50 ppm and show the least variations. The values obtained for Wilkinson's catalyst and our data mark the low-frequency limits found for υ 33 (known exceptions 29 are cases where phosphorus is part of small chelate rings). In combination with the more or less equal splittings, 120-130 Hz, between the major peaks in the 31 P CP/MAS NMR spectrum (Fig.…”

Principles of Spin‐Echo Modulation by J‐Couplings in Magic‐Angle‐Spinning Solid‐State NMR

“…It is less easy to find a physical explanation for why the dipole±dipole coupling also has a stabilising effect on the Jmodulation. Equation (63) is valid in the regime given by Equation (64).…”