Unsymmetrical Platinum(II) Phosphido Derivatives: Oxidation and Reductive Coupling Processes Involving Platinum(III) Complexes as Intermediates

On the Heterogeneous Nature of Cisplatin-1-Methyluracil Complexes: Coexistence of Different Aggregation Modes and Partial Loss of NH3 Ligands as Likely Explanation

The conversion of the 1 : 1-complex of Cisplatin with 1-methyluracil (1MeUH), cis-[Pt(NH3 )2 (1MeU-N3)Cl] (1 a) to the aqua species cis-[Pt(NH3 )2 (1MeU-N3)(OH2 )]+ (1 b), achieved by reaction of 1 a with AgNO3 in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH3 ligands. In dilute aqueous solution, 1 a, and dinuclear compounds cis-[(NH3 )2 (1MeU-N3)Pt(μ-OH)Pt(1MeU-N3)(NH3 )2 ]+ (3) as well as head-tail cis-[Pt2 (NH3 )4 (μ-1MeU-N3,O4)2 ]2+ (4) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of 1 H NMR and ESI-MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ-OH, μ-1MeU, and μ-NH2 bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N2 complex, [Pt(NH3 )(1MeU)(N2 )]+ appears to be formed in gas phase during the ESI-MS experiment. In the presence of Na+ ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non-metalated uracil quartets found in tetrastranded RNA.

Stable mixed-valence diphenylphosphanido bridged platinum(ii)-platinum(iv) complexes

The reaction between [NnBu4][(C6F5)2PtII(μ-PPh2)2PtIV(C^N)(I)2] (C^N = κ2-N,C-benzoquinolinate, 1) and (i) bidentate S^S, N^S and O^O anionic ligands or (ii) monodentate S- N- or O-based anionic ligands was studied in order to investigate the factors that may guarantee the stability of Pt(ii),Pt(iv) mixed-valence dinuclear phosphanido complexes. While reactions of 1 with S^S or N^S ligands afforded stable Pt(ii),Pt(iv) species of general formula [(C6F5)2PtII(μ-PPh2)2PtIV(C^N)(L^S)]x- [(L^S)(x-1) = 2-mercaptopyrimidinate (pymS-), 2-mercaptopyridinate (pyS-), dimethyldithiocarbamate (Me2NCS2-), ethyl xanthogenate (EtOCS2-) and 1,2-benzenedithiolate (PhS22-)], the reaction of 1 with the O^O ligand sodium acetylacetonate gave several products, and no pure Pt(ii),Pt(iv) complex could be isolated. The reaction of monodentate ligands such as PhS-, OH- or N3- with 1 led to a stable Pt(ii),Pt(iv) complex only in the case of N3-. The reaction with OH- afforded the Pt(ii),Pt(ii) complex [(C6F5)2PtII(μ-PPh2)(κ2-O,P-μ-O-PPh2)PtII(C^N)]- (8) deriving from reductive coupling of a diphenylphosphanide and an O-donor ligand coordinated to the Pt(iv) centre, while the reaction with PhS- produced the unstable Pt(ii),Pt(iv) complex [NnBu4][(C6F5)2PtII(μ-PPh2)2PtIV(C^N)(PhS)2] (11) that evolved in solution to the Pt(ii),Pt(ii) species [NnBu4][(C6F5)2PtII(μ-PPh2)2PtII(C^N)] (9) by elimination of diphenyldisulfide. Thus, the stability of mixed valence Pt(ii),Pt(iv) phosphanide complexes is affected by several concurrent factors, including the chelating effect of the ligands and the type of ligating atoms.

31P and 195Pt solid-state NMR and DFT studies on platinum(i) and platinum(ii) complexes

³¹P and ¹⁹⁵Pt solid state NMR spectra on anti-[(PHCy)ClPt(μ-PCy₂)₂Pt(PHCy)Cl] (3) and [(PHCy₂)Pt(μ-PCy₂)(κ²P,O-μ-POCy₂)Pt(PHCy₂)] (Pt–Pt) (4) were recorded under CP/MAS conditions (³¹P) or with the CP/CPMG pulse sequence (¹⁹⁵Pt) and compared to data obtained by relativistic DFT calculations of ³¹P and ¹⁹⁵Pt CS tensors and isotropic shielding at the ZORA Spin Orbit level.

Polynuclear platinum phosphanido/phosphinito complexes: formation of P-O and P-O-P bonds through reductive coupling processes

A mixture of the asymmetric complexes of formula [(RF)2Pt(μ-Ph2PO)(μ-PPh2)Pt(μ-PPh2)2Pt(solv)(solv')] [(1-(solv)(solv')] (solv, solv' = acetone, H2O, CH3CN) has been prepared by reaction of [(RF)2Pt(II)(μ-PPh2)2Pt(II)(μ-PPh2)2Pt(II)(NCCH3)2] with AgClO4 in CH3CN/acetone. The lability of the Pt-solvent bonds allows the displacement of the coordinated solvent molecules by dppm or Cl(-) and the isolation of the tri- or hexanuclear phosphanido/phosphinito Pt(ii) complexes [(C6F5)2Pt(μ-PPh2)(μ-PPh2O)Pt(μ-PPh2)2Pt(dppm)] (2) or [NBu4]2[(C6F5)2Pt(μ-PPh2)(μ-PPh2O)Pt(μ-PPh2)2Pt(μ-Cl)2Pt(μ-PPh2)2Pt(μ-PPh2)(μ-PPh2O)Pt(C6F5)2] (as a mixture of the two possible isomers 4a and 4b). Complex 2 reacts with AgClO4 to form the tetranuclear derivative [(C6F5)2Pt(μ-PPh2)(μ-PPh2O)Pt(μ-PPh2)2Pt(dppm)Ag(OClO3)] (3), which displays two Pt-Ag donor-acceptor bonds. The mixture of the hexanuclear isomers 4a-4b reacts with Tl(acac) producing the acetylacetonato complex [NBu4][(C6F5)2Pt(μ-PPh2)(μ-PPh2O)Pt(μ-PPh2)2Pt(acac)] (5) which, upon reaction with HCl, yields back the mixture of 4a-4b. The reaction of 4a-4b with PPh3 produces [NBu4][(C6F5)2Pt(μ-PPh2)(μ-PPh2O)Pt(μ-PPh2)2Pt(Cl)(PPh3)] (6) as a mixture of isomers with the chloro ligand located syn (6a) or anti (6b) to the PPh2O(-) group. Either the reaction of 6 with AgClO4 or the treatment of 5 with HPPh3ClO4 results in the formation of the species [(C6F5)2Pt(II)(μ-PPh2)2Pt(I)(μ-PPh2OPPh2)Pt(I)(PPh3)] (7) (44 VEC), which can be explained as the consequence of a PPh2O/PPh2 reductive coupling and a rearrangement of ligands in the molecule generating a Pt(ii),Pt(i),Pt(i) compound. All complexes were characterised in the solid state by XRD (only one of the isomers, in the cases of 4 and 6) and in solution by NMR spectroscopy.

Nucleophilicity and P-C Bond Formation Reactions of a Terminal Phosphanido Iridium Complex

The diiridium complex [{Ir(ABPN2)(CO)}2(μ-CO)] (1; [ABPN2](-) = [(allyl)B(Pz)2(CH2PPh2)](-)) reacts with diphenylphosphane affording [Ir(ABPN2)(CO)(H) (PPh2)] (2), the product of the oxidative addition of the P-H bond to the metal. DFT studies revealed a large contribution of the terminal phosphanido lone pair to the HOMO of 2, indicating nucleophilic character of this ligand, which is evidenced by reactions of 2 with typical electrophiles such as H(+), Me(+), and O2. Products from the reaction of 2 with methyl chloroacetate were found to be either [Ir(ABPN2)(CO)(H)(PPh2CH2CO2Me)][PF6] ([6]PF6) or [Ir(ABPN2)(CO)(Cl)(H)] (7) and the free phosphane (PPh2CH2CO2Me), both involving P-C bond formation, depending on the reaction conditions. New complexes having iridacyclophosphapentenone and iridacyclophosphapentanone moieties result from reactions of 2 with dimethyl acetylenedicarboxylate and dimethyl maleate, respectively, as a consequence of a further incorporation of the carbonyl ligand. In this line, the terminal alkyne methyl propiolate gave a mixture of a similar iridacyclophosphapentanone complex and [Ir(ABPN2){CH═C(CO2Me)-CO}{PPh2-CH═CH(CO2Me)}] (10), which bears the functionalized phosphane PPh2-CH═CH(CO2Me) and an iridacyclobutenone fragment. Related model reactions aimed to confirm mechanistic proposals are also studied.

Reactions of trinuclear platinum clusters with electrophiles: ionisation isomerism with [Pt3(μ2-I)(μ-PPh2)2(PPh3)3]I and [Pt3(μ-PPh2)2I2(PPh3)3]. Structures of [Pt3(μ2-Cl)(μ-PPh2)2(PPh3)3]PF6, [Pt3(μ-PPh2)2I2(PPh3)3] and of the Pt–Ag cluster [Pt3{μ3-AgBF4}(μ2-I)(μ-PPh2)2(PPh3)3]BF4

Reactions of the mixed-valence cluster [Pt₃(μ-PPh₂)₃Ph(PPh₃)₂] with various electrophiles have been investigated.

Di- and trinuclear phosphido-bridged platinum complexes. Crystal structures of [Pt{CH(2)=CHC(O)OMe}(PPh(3))(2)], trans-[Pt(2)(micro-PPh(2))(2)I(2)(PPh(3))(2)] and cis,cis,cis-[Pt(3)(mu-I)(2)(mu-PPh(2))(2)Cl(0.5)I(1.5)(PPh(3))(2)]

The readily available Pt(0) methyl acrylate complex [Pt{CH2CHC(O)OMe}(PPh3)2] (2) allows access to the known, mixed-valence trinuclear cluster [Pt3(mu-PPh2)3Ph(PPh3)2] (3) in 64% yield. Oxidation of 3 with 2 equivalents of I2 afforded the new trinuclear complex [Pt3(mu-I)2(mu-PPh2)2I2(PPh3)2] (4) whose molecular structure is similar to that of the related compound of empirical formula [Pt3(mu-I)2(mu-PPh2)2Cl0.5I1.5(PPh3)2] ( 5) which has been generated by oxidation of 3 with successively 1 equivalent of I2 and 1 equivalent of C6H5ICl2. In these complexes, the four halogen atoms lie on the same side of the almost aligned platinum atoms and the nearly square-planar coordination planes of the metal atoms adopt a japanese screen, chair-like conformation. The reaction of the dinuclear, metal-metal bonded Pt(I)-Pt(I) complex [Pt2(mu-PPh2)2(PPh3)2] with one equivalent of I2 afforded the Pt(II) complex [Pt2(mu-PPh2)2I2(PPh3)2] (6). The molecular structures of complexes 2 x CH2Cl2, [Pt3(mu-I)2(mu-PPh2)2(I1.3Cl0.7)(PPh3)2][Pt3(mu-I)2(mu-PPh2)2(I1.7Cl0.3)(PPh3)2] x C6H5Cl x 3CH2Cl2 (5A x 5B x C6H5Cl x 3CH2Cl2) and 6 have been established by single crystal X-ray diffraction studies.