Cooperation between Cis and Trans Influences in cis-Pt^II(PPh₃)₂ Complexes: Structural, Spectroscopic, and Computational Studies

Abstract

The relevance of cis and trans influences of some anionic ligands X and Y in cis-[PtX(2)(PPh(3))(2)] and cis-[PtXY(PPh(3))(2)] complexes have been studied by the X-ray crystal structures of several derivatives (X(2) = (AcO)(2) (3), (NO(3))(2) (5), Br(2) (7), I(2) (11); and XY = Cl(AcO) (2), Cl(NO(3)) (4), and Cl(NO(2)) (13)), density functional theory (DFT) calculations, and one bond Pt-P coupling constants, (1)J(PtP). The latter have allowed an evaluation of the relative magnitude of both influences. It is concluded that such influences act in a cooperative way and that the cis influence is not irrelevant when rationalizing the (1)J(PtP) values, as well as the experimental Pt-P bond distances. On the contrary, in the optimized geometries, evaluated through B3LYP/def2-SVP calculations, the cis influence was not observed, except for compounds ClPh (21), Ph(2) (22), and, to a lesser extent, Cl(NO(2)) (13) and (NO(2))(2) (14). A natural bond order analysis on the optimized structures, however, has shown how the cis influence can be related to the s-character of the Pt hybrid orbital involved in the Pt-P bonds and the net atomic charge on Pt. We have also found that in the X-ray structures of cis-[PtX(2)(PPh(3))(2)] complexes the two Pt-X and the two Pt-P bond lengths are different each other and are related to the conformation of the phosphine groups, rather than to the crystal packing, since this feature is observed also in the optimized geometries.

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

“…We have been able to discriminate the two influences, showing that the former, although of lower importance, is by no means irrelevant and must be taken into account when rationalising 1 J PtP as well as Pt-P bond distances. We could also justify the sequences of both influences in terms of Pt-P bonding and charge on Pt [14].…”

“…Thus X-ray derived M-L bond lengths may be affected by crystal packing and conformational effects and only few M-L bond stretches can be unambiguously assigned (M-H, certain M-Cl and few others); CO stretching frequencies have also been used [13]. NMR investigations are usually based on the values of one bond coupling constants, which can be considered an estimate of the M-L bond strength [1,[13][14][15][16][17][18][19], but this technique can be used only when both M and the donor atom of L are NMR active ( 195 Pt-31 P, 103 Rh-31 P, etc.). 2 J MC and 3 J MH have also been employed [1,20].…”

“…A second paper [14] dealt with the cis-[PtXY(PPh 3 ) 2 ] isomers (type B of Scheme 1). Here each P atom experiences the cis influence of a PPh 3 group, the trans influence of X and the cis influence of Y (or the other way round).…”

“…The difference between 1 J PtP of the Cl derivative with that of a compound with a given X, gives an estimate of such ability, i.e. how much X influences the Pt-P bonds (either cis or trans) with respect of Cl [14,[10][11][12][13][14][15][16][17][18][19][20][21][22].…”

Synthesis and Characterization of Pentanuclear Complexes Composed of Pairs of Macrocyclic Ni2L and Zn2L Complexes Linked by cis‐[PtCl2(dppba)2] and trans‐[RhCl(CO)(dppba)2] [dppba = (4‐Diphenylphosphanyl)benzoate, L = Macrocyclic Ligand]

“…They compare well with the values found for the parent triphenyl phosphine complexes. [17][18][19][20][21][22][23] [17] and trans isomers. [16] The 1 H NMR spectrum of the [Zn 2 L(dppba)] + complex 6 ( Figure 2) displays a single signal set indicating the presence of just one isomer in solution.…”