Comparing Main Group and Transition-Metal Square-Planar Complexes of the Diselenoimidodiphosphinate Anion: A Solid-State NMR Investigation of M[N(ⁱPr₂PSe)₂]₂(M = Se, Te; Pd, Pt)

Abstract

A comparison of the square-planar complexes of group 10 (Pd(II), Pt(II)) and 16 (Se(II), Te(II)) centers with the tetraisopropyldiselenoimidodiphosphinate anion, [N((i)Pr2PSe)2](-), is made on the basis of the results of a solid-state (31)P, (77)Se, (125)Te, and (195)Pt NMR investigation. Density functional theory calculations of the respective chemical shift and (14)N electric field gradient tensors in these compounds complement the experimental results. The NMR spectra were analyzed to determine the respective phosphorus, selenium, tellurium, and platinum chemical shift tensors along with numerous indirect spin-spin coupling constants. Special attention was given to observed differences in the NMR parameters for the transition metal and main-group square-planar complexes. Residual dipolar coupling between (14)N and (31)P, not observed in the solid-state (31)P NMR spectra of the Pd(II) and Pt(II) complexes, was observed at 4.7 and 7.0 T for M[N((i)Pr 2PSe)2]2(M = Se, Te) yielding average values of R((31)P, (14)N)eff = 890 Hz, CQ((14)N) = 2.5 MHz, (1) J( (31)P, (14)N) iso= 15 Hz, alpha = 90 degrees , beta = 17 degrees . The span, Omega, and calculated orientation of the selenium chemical shift tensor for the diselenoimidodiphosphinate anion is found to depend on whether the selenium is located within a pseudoboat or distorted-chair MSe 2P 2N six-membered ring. The largest reported values of (1)J((77)Se, (77)Se) iso, 405 and 435 Hz, and (1)J((125)Te, (77)Se)iso, 1120 and 1270 Hz, were obtained for the selenium and tellurium complexes, respectively; however, in contrast a correspondingly large value of (1)J((195)Pt, (77)Se)iso was not found. The chemical shift tensors for the central atoms, Se(II) and Te(II), possess positive skews, while for Pt(II) its chemical shift tensor has a negative kappa. This observed difference for the shielding of the central atoms has been explained using a qualitative molecular orbital approach.

Solid-state selenium-77 NMR

“…Similarly consistent values of one-bond coupling constants between 77 Se and 113 Cd, 119 Sn,or 199 Hg are found between solid-state 77 Se NMR spectra, Table 9, and solution 77 Se NMR [17]; however, the values of 1 J( 125 Te, 77 Se) iso in Te[N( i Pr 2 PSe) 2 ] 2 , ±1120 and 1270 Hz, are significantly larger in magnitude than any found previously [211]. The 110 Hz magnitude for 1 J( 77 Se, 35 Cl) iso obtained for Ph 2 SeCl 2 appears to be the only reported coupling between selenium and chlorine via solid-state or solution NMR spectroscopy [80].…”

“…The values of 1 J( 77 Se, 77 Se) iso obtained, Fig. 13a and Table 9, appear to be the largest one-bond selenium-selenium coupling constants reported [211].…”

“…16e. The skew of the corresponding selenium chemical shift tensor is +0.32, which is contrasted with the negative skew found for the 195 Pt chemical shift tensor in Pt[N( i Pr 2 PSe) 2 ] 2 , and rationalized using qualitative molecular orbital theory [211]. The values of 1 J( 77 Se, 77 Se) iso obtained, Fig.…”

“…Values of 1 J( 77 Se, 31 P) iso for 3,5-dimethyl-1,2,4-triselena-3,5-diphospholane-3,5-diselone, À340 and À350 Hz [109], are similar to those of bis(organothiaphosphoryl) diselenides, À355 to À532 Hz [206][207][208][209], see Table 5. Table 11 [210,211]. The selenium chemical shift parameters for the M[N( i Pr 2 PSe) 2 ] 2 (M = Zn, Cd, Hg) complexes, which are single-source precursors for metal selenide materials, are all very similar given the chemical shift range of selenium [210].…”

“…The selenium chemical shift parameters for the M[N( i Pr 2 PSe) 2 ] 2 (M = Zn, Cd, Hg) complexes, which are single-source precursors for metal selenide materials, are all very similar given the chemical shift range of selenium [210]. In a subsequent investigation, the solid-state NMR parameters of the group 10 and 16 square planar complexes, M[N( i Pr 2 PSe) 2 ] 2 (M = Pd, Pt; Se, Te) have been contrasted [211]. One conclusion from these studies is that the span, X, of the selenium chemical shift tensor is sensitive to the conformation of the six-membered MSe 2 P 2 N ring.…”