Hydrido Phosphanido Bridged Polynuclear Complexes Obtained by Protonation of a Phosphinito Bridged Pt(I) Complex with HBF₄ and HF

Abstract

The protonation of the phosphinito-bridged Pt(I) complex [(PHCy(2))Pt(μ-PCy(2)){κ(2)P,O-μ-P(O)Cy(2)}Pt(PHCy(2))](Pt-Pt) (1) by aqueous HBF(4) or hydrofluoric acid leads selectively to the hydrido-bridged solvento species syn-[(PHCy(2))(H(2)O)Pt(μ-PCy(2))(μ-H)Pt(PHCy(2)){κP-P(OH)Cy(2)}](Y)(2)(Pt-Pt) ([2-H(2)O]Y(2)) {Y = BF(4), F(HF)(n)} when an excess of acid was used. On standing in halogenated solvents, complex [2-H(2)O](BF(4))(2) undergoes a slow but complete isomerization to [(PHCy(2))(2)Pt(μ-PCy(2))(μ-H)Pt{κP-P(OH)Cy(2)}(H(2)O)](BF(4))(2)(Pt-Pt) ([4-H(2)O][BF(4)](2)) having the P(OH)Cy(2) ligand trans to the hydride. The water molecule coordinated to platinum in [2-H(2)O][BF(4)](2) is readily replaced by halides, nitriles, and triphenylphosphane, and the acetonitrile complex [2-CH(3)CN][BF(4)](2) was characterized by XRD analysis. Solvento species other than aqua complexes, such as [2-acetone-d(6)](2+) or [2-CD(2)Cl(2)](2+) were obtained in solution by the reaction of excess etherate HBF(4) with 1 in the relevant solvent. The complex [2-H(2)O](Y)(2) [Y = F(HF)(n)] spontaneously isomerizes into the terminal hydrido complexes [(PHCy(2))Pt(μ-PCy(2)){κ(2)P,O-μ-P(O)Cy(2)}Pt(H)(PHCy(2))](Y)(Pt-Pt) ([6](Y)). In the presence of HF, complex [6](Y) transforms into the bis-phosphanido-bridged Pt(II) dinuclear complex [(PHCy(2))(H)Pt(μ-PCy(2))(2)Pt{κP-P(OH)Cy(2)}](Y)(Pt-Pt) ([7](Y)). When the reaction of 1 with HF was carried out with diluted hydrofluoric acid by allowing the HF to slowly diffuse into the dichloromethane solution, the main product was the linear 60e tetranuclear complex [(PHCy(2)){κP-P(O)Cy(2)}Pt(1)(μ-PCy(2))(μ-H)Pt(2)(μ-PCy(2))](2)(Pt(1)-Pt(2)) (8). Insoluble compound 8 is readily protonated by HBF(4) in dichloromethane, forming the more soluble species [(PHCy(2)){κP-P(OH)Cy(2)}Pt(1)(μ-PCy(2))(μ-H)Pt(2)(μ-PCy(2))](2)(BF(4))(2)(Pt(1)-Pt(2)) {[9][BF(4)](2)}. XRD analysis of [9][BF(4)](2)·2CH(2)Cl(2) shows that [9](2+) is comprised of four coplanar Pt atoms held together by four phosphanido and two hydrido bridges. Both XRD and NMR analyses indicate alternate intermetal distances with peripheral Pt-Pt bonds and a longer central Pt···Pt separation. DFT calculations allow tracing of the mechanistic pathways for the protonation of 1 by HBF(4) and HF and evaluation of their energetic aspects. Our results indicate that in both cases the protonation occurs through an initial proton transfer from the acid to the phosphinito oxygen, which then shuttles the incoming proton to the Pt-Pt bond. The different evolution of the reaction with HF, leading also to [6](Y) or 8, has been explained in terms of the peculiar behavior of the F(HF)(n)(-) anions and their strong basicity for n = 0 or 1.

A Hydrido η1-Alkynyl Diplatinum Complex Obtained from a Phosphinito Phosphanido Complex and Trimethylsilylacetylene

“…The most striking evidence revealing the transformation of the POCy2 ligand into P(OH)Cy2 is the presence, in the 1 H NMR spectrum of [3]BF4, of a broad peak at δ 6.71 ascribable to the POH proton. Moreover, as reported in related hydrido bridged diplatinum phosphinito species, [3,4] the protonation of the POCy2 ligand provokes a high field shift of the 1 H NMR hydride resonance (from δ −4.46 (in 2) to δ −5.83 (in [3]BF4)) and a low field shift of the phosphinito 31 P NMR resonance (from δ 77.0 (in 2) to δ 124.3 (in [3]BF4)). IR and 13 C NMR data confirmed the presence of the η 1 -acetylide bonded to Pt 1 in [3]BF4.…”

“…The signal at δ 120.9 is ascribable to a bridging phosphanide subtending a Pt-Pt bond [22], while the signal at δ 77.0 is diagnostic of a dicyclohexylphosphinite P(O)Cy2 ligand bonded to Pt through the P atom. In fact, Pt-P(O)Cy2 31 P NMR resonances fall in the range of 75-90 ppm, while their protonated analogues Pt-P(OH)Cy2 give 31 P NMR signals in the range of 115-135 ppm [3,4,23]. The remaining signals (δ 13.7 and δ 2.8) are ascribed to terminal PHCy2 ligands.…”

“…It is now well established that the mixed bridge phosphinito-phosphanido Pt(I) complex [(PHCy2)Pt 1 (μ-PCy2){κP,O-μ-P(O)Cy2}Pt 2 (PHCy2)](Pt-Pt) (1) [1] exhibits an amphiphilic behavior, in that it reacts with both nucleophiles (with initial attack at the Pt 1 center) [2] and electrophiles (with initial attack at the O atom) [3,4]. In particular, reaction of 1 with HX Brønsted acids affords, with the exception of HF, [4] dinuclear compounds endowed with a bridging hydride, a bridging dicyclohexylphosphanide and a covalent bond between Pt 1 and the X residue (Scheme 1).…”

Uncovering Intramolecular π‐Type Hydrogen Bonds in Solution by NMR Spectroscopy and DFT Calculations

“…The existence of a π‐type hydrogen bond between the PO−H and the C≡C triple bond in solution is also suggested by the sharpness of the 31 P NMR signal of the P 4 HCy 2 ligand. In fact, for systems analogous to 2 , the 31 P NMR signal of the P 4 HCy 2 ligand is expected to be quite broad when the P(OH)Cy 2 in the cis position can freely rotate about the Pt−P bond, and relatively sharp when the rotation of the P(OH)Cy 2 ligand is hindered due to the formation of the PO⋅⋅⋅H⋅⋅⋅X bridge (X=Lewis base) …”

“…The existence of a p-type hydrogen bond between the POÀ Ha nd the CCt riple bond in solution is also suggestedb yt he sharpnesso ft he 31 PNMR signalo ft he P 4 HCy 2 ligand.I nf act, for systems analogoust o2,t he 31 PNMR signal of the P 4 HCy 2 ligand is expected to be quite broad when the P(OH)Cy 2 in the cis positionc an freely rotate about the PtÀPb ond, [21] and rela-tively sharpw hen the rotationo ft he P(OH)Cy 2 ligand is hindered due to the formationo ft he PO···H···X bridge (X = Lewis base). [22][23][24][25][26] Another clue to the presence of the p-type hydrogen bond derives from the analysis of the 1 H-195 Pt HMQC spectrum of 2 ( Figure 1) displaying, besides the correlation between the Cy 2 PH protons and the 195 Pt atoms to which the phosphanes are bonded, intense cross peaks between the POH protona nd Pt 1 (but not Pt 2 ).…”