Solution Behavior and Structural Diversity of Bis(dialkylphosphino)methane Complexes of Palladium

Abstract

The preparation of dipalladium complexes containing sterically nondemanding diphosphine (P-P) ligands of the type R(2)PCH(2)PR(2) where R = Me (dmpm) or Et (depm) is reported. Variable-temperature (1)H NMR spectra of the Pd(I)(2) complexes Pd(2)X(2)(dmpm)(2) (X = Cl, Br, or I; the P-P ligands in the Pd(2) complexes are always bridged, but for convenience, the micro -symbol is omitted) show the complexes to be fluxional in solution, the barriers to a ring-flipping process being DeltaG( double dagger ) = 37.9, 39.0, and 43.2 +/- 0.9 kJ mol(-)(1) for the chloro, bromo, and iodo complexes, respectively. Treatment of Pd(2)X(2)(P-P)(2) (X = Cl or Br) with X(2) generates the stable, face-to-face Pd(II)(2) derivatives trans-Pd(2)X(4)(P-P)(2), while oxidation of Pd(2)I(2)(P-P)(2) complexes with I(2) generates a new type of symmetrically di-iodo-bridged, five-coordinate complexes Pd(2)I(2)(micro -I)(2)(dmpm)(2) and Pd(2)I(2)(micro -I)(2)(depm)(2). The molecular crystal structures of four dipalladium(II) complexes are described: trans-Pd(2)Cl(4)(dmpm)(2).2CHCl(3), trans-Pd(2)Br(4)(dmpm)(2), trans-Pd(2)Cl(4)(depm)(2), and Pd(2)I(2)(micro -I)(2)(dmpm)(2). Solution NMR and UV-vis absorption spectra are consistent with the solid-state structures determined by X-ray diffraction. The stability of the dimeric Pd(II) complexes is attributed primarily to ligand steric factors.

Trans-chelating diphosphines, the elusive ligands!

“…The same types of structures A and B have been also observed with short chain diphosphines, even when they contained only one carbon in the backbone! (the large class of A-frame complexes belongs to this group [205][206][207][208], e.g. PdCl 2 (Ph 2 PCH 2 PPh 2 ) 2 type B, P-P distance 3.3Å).…”

Organo-Metallic Compounds: Novel Molecules in Cancer Therapy

“…DNA intercalation and/or cleavage) may be responsible for their biological activity. DNA binding studies indicate that (η 6 -C 6 Me 6 )Ru(II) compounds containing dpq or particularly dppz ligands are good metallointercalators but that the dppn ligand is too large to support stable intercalation between the base pairs of the double helix [34][35][36][37][38][39][40][41][42]. The in vitro and in vivo assessment of a series of η 6 -arene ruthenium complexes containing a pta ligand (pta = 1,3,5-triaza-7-phosphaadamantane) were evaluated as anticancer agents [44].…”

Reactivity of the bridged-sulfide complex Pd2Cl2(μ-S)(μ-dmpm)2toward electrophiles

“…4a, 38 A brown solid, isolated from the reaction of Pd 2 I 2 (m-S)(dmpm) 2 (2c) with m-CPBA, contained ~95% of an unidentified species (Z) that was associated with a singlet in CD 2 Cl 2 at d P -18.1, a CH 2 quintet at d H 3.57 (J PH = 4.3 Hz), and a CH 3 singlet resonance at d H 2.11, implying a symmetric species that is not Pd 2 I 2 (m-I) 2 (dmpm) 2 . 26 This (m-I) 2 complex is often formed as an impurity during reactions involving Pd 2 I 2 (dmpm) 2 (1c) or 2c (e.g. in reactions with MeI, and with I 2 -see below).…”

“…in reactions with MeI, and with I 2 -see below). The brown solid contains small amounts of Pd 2 I 2 (dmpm) 2 (d P -38.4; d H 2.82 qn, J PH = 3.6 Hz), 26 and a further unidentified species (d P -20.5; d H 1.75-1.89 m).…”

“…The "face-to-face" intermediates, trans-[PdX 2 (dppm)] 2 , were also detected in the reaction between Pd 2 X 2 (dppm) 2 and X 2 ; 39 in the corresponding dmpm systems, the analogous X = Cl and Br, yellow complexes were isolated, and the X = I species was isolated as the purple-coloured Pd 2 I 2 (m-I) 2 (dmpm) 2 . 26 Pd X -S)(dppm) X…”