Alberto Albinati

Dispersion‐Driven Hydrogen Bonding: Predicted Hydrogen Bond between Water and Platinum(II) Identified by Neutron Diffraction

We report here the first crystallographic evidence for a hydrogen-bonding-like interaction between a water molecule and a d8 metal ion, based on neutron diffraction. According to our HF and MP2 calculations, the interaction is almost entirely dispersion-driven and thus represents a limiting case of hydrogen bonding. We speculate that for square-planar d8 metal complexes of zero or negative charge, such hydrogen bonding with water molecules might affect the solvolysis mechanism and be at the origin of anomalously slow aquation rate constants previously reported for some PtII complexes.

Facile cycloplatination of nitrogen compounds. Crystal structure of the cycloplatinated Schiff's base tetralone derivative PtCl{(cyclohexyl)NC(CH2)3C6H3 (CO)

Abstract Facile preparative methods for the cycloplatination of benzo[ c ]quinoline ( 1 ), two Schiffs base tetralone compounds, R 1 NC(CH 2 ) 3 C 6 H 4 (R 1 = cyclohexyl ( 2 ), CH 2 ( p -C 6 H 4 OCH 3 ) ( 3 )), and 8-methylquinoline ( 4 ), are given. An extension of these methods leads readily to new cycloplatination chemistry involving use of 1 or 3 or quinoline-8-carboxaldehyde and the cycloplatinated phosphite complex [Pt(μ-Cl){(R 2 O) 2 POC 6 H 4 ]] 2 , R 2 = Et, Ph, to give the complexes Pt(NO 3 )( CN ){P(OPh)(OR) 2 }, where ( CN ) denotes the cycloplatinated nitrogen-ligand. The molecular structure of PtCl{(cyclohexyl)NC(CH 2 ) 3 C 6 H 3 ](CO) has been determined by X-ray diffraction.

Palladium(II) complexes of chiral tridentate nitrogen pybox ligands

A series of mono- and di-cationic palladium(II) complexes containing different chiral tridentate nitrogen ligands, pybox, have been prepared [pybox = 2,6-bis[4′-(S)-iPr (or Ph, or Bz or p-EtOC6H4)oxazoline-2′-yl]pyridine (1–4), respectively]. The molecular structures for two of these, [Pd(CH3CN)(2)](BF4)2 (6) and [Pd(PPh3)(3)](BF4)2 (21g), have been determined by X-ray diffraction and show no major steric hindrance in the fourth coordination position. In connection with the aldol reaction of CNCH2CO2Me with PhCHO, several new isonitrile PdII complexes have also been prepared. It is shown that, under catalytic conditions, the chiral tridentate pybox ligand is completely displaced, thus explaining its failure as a chiral auxiliary. Preparative details for a series of chiral Pd(L)(3)n+(BF4)n (21) complexes [L = 4-methylpyridine, 2,6-dimethylpyridine, 4-methyl aniline, H2NCH2CH(OMe)2, H2NCH2CH2OH, H2N(CH2)5CH3, N3−, HCO2−] Cl−] are given, as are preparative details for some model PdII acetonitrile complexes with chiral phosphorus and nitrogen chelating ligands. For 6, i.e. PdC25H22N4O2B2F8, the crystals are monoclinic with space group P21 (No. 4), a = 13.582(6) A, b = 13.826(6) A, c = 14.667(6) A, β = 97.28(3)°, V = 2732(2) A3, Z = 4. For 21g, i.e. C43H38B2F8N3O2P2Pd, the crystals are orthorhombic with space group, P212121, a = 10.616(4) A, b = 16.774(2) A, c = 23.086(4) A, V = 4111(3) A3, Z = 4.

195Pt, 119Sn and 31P NMR studies of alkyl, aryl and acyl trichlorostannate complexes of platinum(II). The crystal structure of trans-[Pt(SnCl3)(COC6H5)(PEt3)2]

Abstract 195 Pt, 119 Sn and 31 P NMR characteristics of the complexes trans -[Pt(SnCl 3 )(carbon ligand)(PEt 3 ) 2 ] ( 1a - 1e ) are reported, (carbon ligand = CH 3 ( 1a ), CH 2 Ph ( 1b ), COPh ( 1c ), C 6 Cl 5 ( 1d ), C 6 Cl 4 Y ( e ); Y = meta - and para -NO 2 , CF 3 , Br, H, CH 3 , OCH 3 , or Pt(SnCl 3 )(PEt 3 ) 2 . The values of 1 J ( 195 Pt, 119 Sn) vary from 2376 to 11895 Hz with the COPh ligand having the smallest and the C 6 Cl 5 ligand the largest value, making a total range for this coupling constant, when the dimer syn - trans -[PtCl(SnCl 3 )(PEt 3 )] 2 is included, of ca. 33000 Hz. In the meta - and para -substituted phenyl complexes 1 J ( 195 Pt, 119 Sn) (a) is greater for electron-withdrawing substituents, (b) varies more for the meta -substituted derivatives (5634 to 7906 Hz) than for the para analogues (6088 to 7644 Hz) and (c) has the lowest values when the Pt(SnCl 3 )(PEt 3 ) 2 group is the meta - or para -substituent. The direction of the change in 1 J ( 195 Pt, 119 Sn) is opposite to that found for 1 J ( 195 Pt, 119 P). For the aryl complexes linear correlations are observed between δ( 119 Sn), 1 J ( 195 Pt, 119 Sn), 1 J ( 195 Pt, 31 P), 1 J ( 119 Sn, 31 P) and the Hammett substituent constant σ n . δ( 119 Sn) and 1 J ( 195 Pt, 119 Sn) are related linearly to v (Pt-H) in the complexes trans -[PtH(C 6 H 4 Y)(PEt 3 ) 2 ]; δ( 119 Sn) and δ( 1 H) (hydride) are also linearly related. Based on 1 J ( 195 Pt, 119 Sn), the acyl ligand is suggested to have a very large NMR trans influence. The differences in the NMR parameters for ( 1a-e ) are rationalized in terms of differing σ- and π-bonding abilities of the carbon ligands. The structure of 1c has been determined by crystallographic methods. The complex has a slightly distorted square planar geometry with trans -PEt 3 ligands. Relevant bond lengths (A) and bond angles (°) are: PtSn, 2.634(1), PtP, 2.324(4) and 2.329(4), PtC, 2.05(1); PPtP, 170.7(6), SnPtC, 173.0(3), SnPtP, 92.1(1), 91.7(1), PPtC, 88.8(4) and 88.3(4). The PtSn bond separation is the longest yet observed for square-planar platinum trichlorostannate complexes, and would be consistent with a large crystallographic trans influence of the benzoyl ligand. The PtSn bond separation is shown to correlate with 1 J ( 195 Pt, 119 Sn).

Chemistry of PdII complexes containing both BINAP (2′2′-bis(diphenylphosphino)binaphthyl) and a η3-pinene or -allyl ligand. NMR studies on [Pd(η3-C10H15){S(−)BINAP}] (CF3SO3). The crystal structure of [Pd(η3-C10H15)(4,4′-dimethylbipyridine)](CF3SO3)

Abstract One and two-dimensional 1H, 13C and 31P NMR studies on palladium(II) complexes containing η3-C10H15 or η3-C4H7 allyl and S(−)BINAP ligands are reported. Details of the three-dimensional solution structure for [Pd(η3C10H15) {S(−)BINAP}(CF3SO3) based on 1H-2D NOESY and molecular modelling calculations are presented. The structure for the model β-pinene allyl complex [Pd(η3-C10H15)(4,4′-dimethylbipyridine)]CF3SO3) has been determined by an X-ray diffraction study, which reveals that the CH2 terminal allyl carbon is significantly displaced from the N-Pd-N plane.

Single-crystal X-ray and neutron diffraction structure determination and inelastic neutron scattering study of the dihydrogen complex trans-[Ru(H2)(H)(dppe)2][BPh4]

Abstract The structure of the complex trans -[Ru( η 2 -H 2 )(H)(dppe) 2 ][BPh 4 ]( 1 ),dppe = PPh 2 CH 2 CH 2 PPh 2 , has been determined by single-crystal X-ray diffraction at 123 K and neutron diffraction at 12 K. The core of the complex has a distorted octahedral geometry about ruthenium with the dihydrogen ligand trans to hydride and eclipsing a trans -PRuP axis that is bent away front the hydrogens with a PRuP angle of 167.9(4)°. The crystallographically determined H-H distance is 0.83(8) (X-ray) or 0.82(3) (neutron) A. The latter value, where corrected for the shortening caused by the torsional libration of the H 2 ligand, increases to about 0.94 A. The long Ru(H 2 ) distance of 1.81(2) A (neutron), compared to the terminal hydride to ruthenium distance of 1.64(2) A (neutron), is consistent with the lability of the dihydrogen ligand, which is partially lost from the crystal by treatment with vacuum. The analogous iron complex trans-[Fe(η) 2 -H 2 )(H)(dppe) 2 [BPh 4 ]( 2 ) has similar features except that the FeH(H 2 ) distances are much shorter and the H 2 ligand is correspondingly less labile. An inelastic neutron scattering study of the powder of 1 at 5 K reveals two broad inelastic peaks flanking the elastic peak. With the assumption that the dihydrogen librates in a double-minimum potential, the barrier to dihydrogen reorientation is calculated to be 1.0 to 1.4 kcal mol − , depending upon which of the HH distances is used. This barrier is less than that for the iron analog, determined for its BF 4 salt, therefore suggesting that there may be less d π → σ ∗ backbonding in 1 than 2 .

Synthetic methodologies for tripodal phosphines. The preparation of MeSi(CH2PPh2)3 and n-BuSn(CH2PPh2)3 and a comparison of their rhodium(I) and ruthenium(II) coordination chemistry. The X-ray crystal structures of [Rh(NBD){n-BuSn(CH2PPh2)3}](OTf) and [Rh(NBD){MeSi(CH2PPh2)3}](OTf)☆

Abstract The preparation of the new tripodal ligands MeSi(CH2PPh2)3 (Si-triphos) and n-BuSn(CH2PPh2)3 (Sn-triphos) and their complexes of rhodium(I) of the type [Rh(NBD)(tripod)](OTf) (NBD  norbornadiene, OTf  triflate) and of ruthenium(II) of the type [Ru(O2CCF3)2(tripod)], is reported. The coordination chemistry of the new tripodal phosphines, and in particular that of Sn-triphos, differs significantly from that of MeC(CH2PPh2)3 (triphos). A comparison of the X-ray structure of [Rh(NBD)(triphos)](OTf) with those of the new complexes [Rh(NBD)(Sn-triphos)](OTf) and [Rh(NBD)(Si-triphos)](OTf) shows that the steric requirements of the ligands RE(CH2PPh2)3 (E  C, Si and Sn), increas from the carbon to the tin compound. The coordination chemistry of ruthenium(II) indicates that, relative to triphos, Sn-triphos displays an enhanced steric bulk which, however, is not sufficient to stabilize the mononuclear, five-coordinate dichloro complexes.

Synthesis of Ru–Arene complexes of Me-Duphos. X-ray, PGSE NMR diffusion and catalytic studies

Abstract Cationic [RuCl(arene)(Me-Duphos)]Cl complexes, arene=η6-benzene and η6-p-cymene, Me-Duphos=1,2-bis-((2R,5R)-2,5-dimethylphospholano) benzene) have been prepared and studied by X-ray crystallography and NMR spectroscopy. PGSE NMR diffusion studies have been used to recognize (a) ion pairing as a function of solvent and (b) larger molecular volumes. Several arene–Ru-complexes have been shown to be useful catalyst precursors in the hydrolysis of terminal aryl alkynes to afford acetophenones.

Experimental and TDDFT Characterization of the Light-Induced Cluster-to-Iron Charge Transfer in the (Ferrocenylethynyl)-Substituted Trinuclear Platinum Derivative [Pt3(μ-PBut2)3(CO)2(C≡C−Fc)]+

The reaction between Pt(3)(mu-PBu(t)(2))(3)(CO)(2)Cl (2) and ethynylferrocene, in the presence of catalytic amounts of CuI, gives Pt(3)(mu-PBu(t)(2))(3)(CO)(2)C[triple bond]CFc (1), characterized by X-ray crystallography and representing a rare example of the sigma-coordination of an alkynyl moiety to a cluster unit. In a dichloromethane (CH(2)Cl(2)) solution, compound 1 undergoes three consecutive one-electron oxidations, the first of which is assigned to the ferrocene-centered Fe(II)/Fe(III) redox couple. Spectroelectrochemistry, carried out on a solution of 1, shows the presence of a broad band in the near-IR region, growing after the electrochemical oxidation, preliminarily associated with a metal-to-metal charge transfer toward the Fe(III) ion of the ferrocenium unit. Density functional theory (DFT) has been employed to analyze the ground- and excited-state properties of 1 and 1(+), both in the gas phase and in a CH(2)Cl(2) solution. Vertical excitation energies have been computed by the B3LYP hybrid functional in the framework of the time-dependent DFT approach, and the polarizable continuum model has been used to assess the solvent effect. Our results show that taking into account the medium effects together with the choice of an appropriate molecular model is crucial to correctly reproducing the excitation spectra of such compounds. Indeed, the nature of the substituents on P atoms has been revealed to have a key role in the quality of the calculated spectra.

Versatile coordination of 2-pyridinetetramethyldisilazane at ruthenium: Ru(II) vs Ru(IV) as evidenced by NMR, X-ray, neutron, and DFT studies.

The novel disilazane compound 2-pyridinetetramethyldisilazane (1) has been synthesized. The competition between N-pyridine coordination and Si-H bond activation was studied through its reactivity with two ruthenium complexes. The reaction between 1 and RuH(2)(H(2))(2)(PCy(3))(2) led to the isolation of the new complex RuH(2){(eta(2)-HSiMe(2))N(kappaN-C(5)H(4)N)(SiMe(2)H)}(PCy(3))(2) (2) resulting from the loss of two dihydrogen ligands and coordination of 1 to the ruthenium center via a kappa(2)N,(eta(2)-Si-H) mode. Complex 2 has been characterized by multinuclear NMR experiments ((1)H, (31)P, (13)C, (29)Si), X-ray diffraction and DFT studies. In particular, the HMBC (29)Si-(1)H spectrum supports the presence of two different silicon environments: one Si-H bond is dangling, whereas the other one is eta(2)-coordinated to the ruthenium with a J(SiH) value of 50 Hz. DFT calculations (B3PW91) were also carried out to evaluate the stability of the agostic species versus a formulation corresponding to a bis(sigma-Si-H) isomer and confirmed that N-coordination overcomes any stabilization that could be gained by the establishment of SISHA interactions. There is no exchange between the two Si-H bonds present in 2, as demonstrated by deuterium-labeling experiments. Heating 2 at 70 degrees C under vacuum for 24 h, leads to the formal loss of one equivalent of H(2) from 2 and formation of the 16-electron complex RuH{(SiMe(2))N(kappaN-C(5)H(4)N)(SiMe(2)H)}(PCy(3))(2) (3) formulated as a hydrido(silyl) species on the basis of multinuclear NMR experiments. The dehydrogenation reaction is fully reversible under dihydrogen atmosphere. Reaction of Ru(COD)(COT) with 3 equiv of 1 under a H(2) pressure led to the isolation of the new complex RuH{(SiMe(2))N(kappaN-C(5)H(4)N)(SiMe(2)H)}(3) (4) characterized as a hydridotrisilyl complex by multinuclear NMR techniques, X-ray and neutron diffractions, as well as DFT calculations. The (29)Si HMBC experiments confirm the presence of two different silicon atoms in 4, with a signal at -14.64 ppm for three dangling Si-Me(2)H fragments and a signal at 64.94 ppm (correlating with the hydride signal) assigned to three Si-Me(2)N groups bound to Ru. Comparison of DFT and neutron parameters involving the hydride clearly indicates an excellent correlation. The Si-H distance of approximately 2.15 A is much shorter than the sum of the van der Waals radii and typically in the range of a significant interaction between a silicon and a hydrogen atom (SISHA interactions). In 4, three dangling Si-H groups remain accessible for further functionalization.