Impact of Coordination Geometry, Bite Angle, and Trans Influence on Metal–Ligand Covalency in Phenyl-Substituted Phosphine Complexes of Ni and Pd

Abstract

Despite the long-standing use of phosphine and diphosphine ligands in coordination chemistry and catalysis, questions remain as to their effects on metal-ligand bonding in transition metal complexes. Here we report ligand K-edge XAS, DFT, and TDDFT studies aimed at quantifying the impact of coordination geometry, diphosphine bite angle, and phosphine trans influence on covalency in M-P and M-Cl bonds. A series of four-coordinate NiCl2 and PdCl2 complexes containing PPh3 or Ph2P(CH2)nPPh2, where n = 1 (dppm), 2 (dppe), 3 (dppp), and 4 (dppb), was analyzed. The XAS data revealed that changing the coordination geometry from tetrahedral in Ni(PPh3)2Cl2 (1) to square planar in Ni(dppe)Cl2 (2) more than doubles the intensity of pre-edge features assigned to Ni-P and Ni-Cl 1s → σ* transitions. By way of comparison, varying the diphosphine in Pd(dppm)Cl2 (4), Pd(dppp)Cl2 (6), and Pd(dppb)Cl2 (7) yielded Pd-P 1s → σ* transitions with identical intensities, but a 10% increase was observed in the P K-edge XAS spectrum of Pd(dppe)Cl2 (5). A similar observation was made when comparing Ni(dppe)Cl2 (2) to Ni(dppp)Cl2 (3), and DFT and TDDFT calculations corroborated XAS results obtained for both series. Comparison of the spectroscopic and theoretical results to the diphosphine structures revealed that changes in M-P covalency were not correlated to changes in bite angles or coordination geometry. As a final measure, P and Cl K-edge XAS data were collected on trans-Pd(PPh3)2Cl2 (8) for comparison to the cis diphosphine complex Pd(dppe)Cl2 (5). Consistent with phosphine's stronger trans influence compared to chloride, a 35% decrease in the intensity of the Pd-P 1s → σ* pre-edge feature and a complementary 34% increase in Pd-Cl 1s → σ* feature was observed for 8 (trans) compared to 5 (cis). Overall, the results reveal how coordination geometry, ligand arrangement, and diphosphine structure affect covalent metal-phosphorus and metal-chloride bonding in these late transition metal complexes.

Distorted tetrahedral nickel-nitrosyl complexes: spectroscopic characterization and electronic structure

“…The first at 2820.3 eV correspond to the Ni 3d orbitals, while the higher energy features can be correlated with a modest, but not negligible Cl→PPh 3 interligand charge transfer as the Cl 3p orbitals mix with the P-C σ* orbitals of the phosphane ligand through the Ni center. Similar spectral features were detected for compositionally analogous Pd complexes [90], but with square planar coordination environment. Thus, the origin of the higher energy features cannot be correlated with multiplet effects as seen above for the Ni L-edge data.…”

A Comprehensive Investigation of a Zwitterionic GeI Dimer with a 1,2‐Dicationic Core

“…square-planar versus tetrahedral) has am uch larger impact. [47] Although there is a variation in the P-Ge-P bond angle of more than 38 between 1Ge (88.58 (3)), 1GeCl (85.50 (3)), and 2OTf (87.13(3)8)t hey were deemeds uitable standards, with 1GeCl being as tructurals tandard for aG e II centerb ound to ligand [1],a nd compound 2OTf offering ap robe for whethert he anionic backbonei n 1GeCl has an effect on the edge energy.G em etal, GeCl 2 (dioxane), and GeO 2 were used as general standardst o benchmark Ge 0 ,G e II ,and Ge IV ,respectively.…”

“…It should be noted that ag iven oxidation state cannot be fixed to as pecific E 0 because E 0 is also influenced by the ionicc omponent of the EÀE' bond, the coordination number,substituent type(s), and geometry. [36,47,48] Phosphinoborate ligandsa re welld ocumented as being superior s-donors to their neutral analogues. This has typically been demonstrated by monitoring the behavior of charged versus neutral ligands in coordination compounds.…”

Validating the Biphilic Hypothesis of Nontrigonal Phosphorus(III) Compounds

“…Phosphorus K-edge XANES [36] is an ideal elementspecific technique for extracting information concerning electronic structure and chemical bonding in diverse phosphorus compounds. [37][38][39][40][41][42][43][44] Unoccupied frontier orbital energies are measured by excitation of core P1 se lectrons,a nd transitions are governed by the dipole selection rule so that peak intensity correlates to P3 pc haracter in the associated virtual orbitals. [45,46] Fort rismethylanilide P(NMePh) 3 , [47] abenchmark crystalline C 3 -symmetric phosphorous triamide, the PK-edge XANES spectrum exhibits an intense pre-edge feature at 2147.0 eV (Figure 2a,b lue dashes).…”