Quantification of mutual trans influence of ligands in Pd(ii) complexes: a combined approach using isodesmic reactions and AIM analysis

Abstract

Isodesmic reactions of the type Pd(II)Cl(2)X + Pd(II)Cl(3) --> Pd(II)Cl(2) + Pd(II)Cl(3)X have been designed to study the trans influence of a variety of 'X' ligands (X = H(2)O, NH(3), Py, CO, SMe(2), C(2)H(4), AsH(3), PH(3), AsMe(3), PMe(3), PEt(3), ONO(-), F(-), Cl(-), Br(-), N(3)(-), NO(2)(-), OH(-), CN(-), Ph(-), H(-), CH(3)(-), SiH(3)(-)) using density functional theory (MPWB1K) and COSMO continuum solvation model. We find that the isodesmic reaction energy E(1) is a good quantitative measure of the trans influence of X. E(1) showed good linear relationships to trans Pd-Cl bond length and the electron density rho(r) at the (3, -1) bond critical point of the trans Pd-Cl bond. On the basis of E(1) values, ligands are classified into three trans influencing groups, viz. strong, moderate, and weak. Isodesmic reactions of the type Pd(II)Cl(2)X + Pd(II)Cl(2)Y --> Pd(II)Cl(2) + Pd(II)Cl(2)X(Y) with ligands 'X' and 'Y' in the trans positions are also modelled to obtain the energy of the reaction E(2). E(2) is a measure of the mutual trans influence of X and Y and the highest (99.65 kcal mol(-1)) and the lowest (-3.95 kcal mol(-1)) E(2) are observed for X = Y = SiH(3)(-) and X = Y = H(2)O, respectively. Using the E(1) values of X (E(1X)) and Y (E(1Y)), the empirical equation 0.02026(E(1X) + (E(1Y)/radical2))(2) is derived for predicting the E(2) values (standard error = 2.33 kcal mol(-1)). Further, using the rho(r) of the trans Pd-Cl bond in [Pd(II)Cl(3)X](n-) (rho(1X)) and [Pd(II)Cl(3)Y](n-) (rho(1Y)), and a multiple linear regression (MLR) approach with rho(1X), rho(1Y), and rho(1X)rho(1Y) as variables, accurate prediction is made for predicting E(2) of any combination of X and Y (standard error = 2.20 kcal mol(-1)). We also find that the contribution of trans influence to the bond dissociation energy of ligands X or Y in complexes of the type [Pd(II)Cl(2)X(Y)](n-) can be quantified in terms of E(1X) and E(1Y) or the corresponding rho(1X) and rho(1Y). The calculated E(1) values may find use in the development of new trans influence-incorporated force field models for palladium.

The Trans Influence in Unsymmetrical Pincer Palladacycles: An Experimental and Computational Study

“…The topological analysis of the electron density at the bond critical point, and the structure determination, show that the strength of the trans influence is in the order P > S > N. This is in agreement with previous work [40,42].…”

“…This is in good agreement with that of Kapoor and Kakkar's study [40] into the square planar Pt complexes using DFT calculations. Their results showed a trans influence series in order of P > S > N. Moreover, Sajith and Suresh [42] studied the correlation between ρ(r) and trans influence in a square planar Pd complex, showing good linear relation between ρ(r) and trans influence, with a trans influence series of PMe 3 > SMe 2 > NH 3 .…”

Quantification of cis and trans influences in [PtX(PPh3)3]+ complexes. A 31P NMR study

“…All complexes were all isolated as their BF 4 (5) and NO 2 (6a and 6b) complexes were obtained by metathesis reactions, treating 1 with the appropriate silver salt. The reaction with AgNO 2 (performed under strict anaerobic conditions since nitrite is easily oxidised under these conditions [14]) gave a solid which analysed correctly for [Pt(NO 2 )(PPh 3 ) 2 ](BF 4 ), whose IR spectrum showed bands suggestive of the presence of the nitro and nitrito linkage isomers [33] (see Section 2).…”

“…cis and trans influences of a ligand X can be defined as the ability of that ligand to weaken the bond between a metal and a ligand L, respectively, cis or trans to X [1][2][3][4][5][6]. The comprehension of these influences is therefore important for understanding and rationalising some properties of square planar and octahedral transition metal complexes.…”

“…The comprehension of these influences is therefore important for understanding and rationalising some properties of square planar and octahedral transition metal complexes. These include stability, occurrence of geometrical isomers, bond strengths, as well as ligand reactivity (through the link with the cis and trans effects) [1][2][3][4][5]. Because of such importance, these influences have been the subject of many investigations from their early recognition [6] to the present days [2,3,[7][8][9][10].…”