Biomedical subjects

Maurizio Varrone

Publications and source records attributed to Maurizio Varrone.

4 recordsLinked to original sources

PubMed2004

Sterically hindered electron-withdrawing ligands: the reactions of N-carbazolyl phosphines with rhodium and palladium centres.

The series of N-carbazolyl phosphines PPh(3-n)(NC(12)H(8))(n)(n= 1, L1; n= 2, L2; n= 3, L3) has been synthesised using BuLi to generate the N-carbazolyl lithium salt, followed by reaction with the appropriate chlorophosphine. The reactions between [Rh(mu-Cl)(CO)(2)](2) and four equivalents of L1 or L2 gave [RhCl(CO)(L1)(2)] 1 and [RhCl(CO)(L2)(2)] 2, though attempts to synthesise the analogous complex using L3 resulted in the formation of [Rh(mu-Cl)(CO)(L3)](2) 3 instead. The inability of L3 to cleave the chloride bridges can be related to its considerable steric requirements. The electronic properties of L1-3 were assessed by comparison of the nu(CO) values of the [Rh(acac)(CO)(L1-3)] complexes 4-6. The increase in number of N-carbazolyl substituents at the phosphorus atom results in a decrease of the sigma-donor and increase in the pi-acceptor character in the order L1 < L2 < L3. In the reactions of L1-3 with [PdCl(2)(cod)] only L1 was able to displace cod from the metal centre and form [PdCl(2)(L1)(2)] 7. The use of [PdCl(2)(NCMe)(2)] instead of [PdCl(2)(cod)] resulted in the formation of the complexes [PdCl(2)(L1)(2)] 7 from L1, the cyclometallated complex [Pd(mu-Cl)[P(NC(12)H(8))(2)(NC(12)H(7))-kappa(2)P,C]](2) 8 from L3 , and a mixture of [PdCl(2)(L2)(2)] 9 and [Pd(mu-Cl)[PPh(NC(12)H(8))(NC(12)H(7))-kappa(2)P,C]](2) 10 from L2 . The reaction of L3 with [Pd(OAc)(2)] produced the cyclometallated complex [Pd(mu-O(2)CCH(3))[P(NC(12)H(8))(2)(NC(12)H(7))-kappa(2)P,C]](2) 11. The reaction of L3 with [Pd(2)(dba)(3)].CHCl(3) produced the 14-electron complex [Pd(L3)(2)] 12. The X-ray crystal structures of six complexes are reported, all of which show the presence of C-H...Pd hydrogen bonding.

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PubMed2003

Diphosphines possessing electronically different donor groups: synthesis and coordination chemistry of the unsymmetrical Di(N-pyrrolyl)phosphino-functionalized dppm analogue Ph2PCH2P(NC4H4)2.

The unsymmetrical diphosphinomethane ligand Ph(2)PCH(2)P(NC(4)H(4))(2) L has been prepared from the reaction of Ph(2)PCH(2)Li with PCl(NC(4)H(4))(2). The diphenylphosphino group can be selectively oxidized with sulfur to give Ph(2)P(S)CH(2)P(NC(4)H(4))(2) 1. The reaction of L with [MCl(2)(cod)] (M = Pd, Pt) gives the chelate complexes [MCl(2)(L-kappa(2)P,P')] (2, M = Pd; 3, M = Pt) in which the M-P bond to the di(N-pyrrolyl)phosphino group is shorter than that to the corresponding diphenylphosphino group. However, the shorter Pd-P bond is cleaved on reaction of 2 with an additional 1 equiv of L to give [PdCl(2)(L-kappa(1)P)(2)] 4. Complex 4 reacts with [PdCl(2)(cod)] to regenerate 2, and with [Pd(2)(dba)(3)].CHCl(3) to give the palladium(I) dimer [Pd(2)Cl(2)(mu-L)(2)] 5, which exists in solution and the solid state as a 1:1 mixture of head-to-head (HH) and head-to-tail (HT) isomers. The palladium(II) dimer [Pd(2)Cl(2)(CH(3))(2)(mu-L)(2)] 6, formed by the reaction of [PdCl(CH(3))(cod)] with L, also exists in solution as a mixture of HH and HT isomers, although in this case the HT isomer prevails at low temperature and crystallizes preferentially. Complex 6 reacts with TlPF(6) to give the A-frame complex [Pd(2)(CH(3))(2)(mu-Cl)(mu-L)(2)]PF(6) 7. The reaction of L with [RuCp*(mu(3)-Cl)](4) leads to the dimer [Ru(2)Cp*(2)(mu-Cl)(2)(mu-L)] 8, for which the enthalpy of reaction has been measured. The reaction of L with [Rh(mu-Cl)(cod)](2) gives a mixture of compounds from which the dimer [Rh(2)(mu-Cl)(cod)(2)(mu-L)]PF(6) 9 can be isolated. The crystal structures of 2.CHCl(3), 3.CH(2)Cl(2), 4, 5.(1)/(4)CH(2)Cl(2), 6, 7.2CH(2)Cl(2), 8, and 9.CH(2)Cl(2) are reported.

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PubMed2002

(+/-)-6-tert-butyl-8-hydroxymethyl-2-phenyl-4H-1,3-benzodioxin and 2,2,2',2',6,6'-hexamethyl-8,8'-methylenebis(4H-1,3-benzodioxin).

Two compounds containing 1,3-benzodioxin groups are reported, namely (+/-)-6-tert-butyl-8-hydroxymethyl-2-phenyl-4H-1,3-benzodioxin, C(19)H(22)O(3), (I), and 2,2,2',2',6,6'-hexamethyl-8,8'-methylenebis(4H-1,3-benzodioxin), C(23)H(28)O(4), (II). The hydroxy groups of neighbouring molecules in (I) are hydrogen bonded to each other, giving rise to double-row chains. The molecule in (II) adopts a 'butterfly' conformation, with the O atoms in distal positions. In both compounds, the dioxin rings are in distorted half-chair conformations.

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PubMed2002

Selective cleavage of P-N bonds and the conversion of rhodium N-pyrrolyl phosphine complexes into diphosphoxane-bridged dimers.

Rhodium(I) complexes trans-[RhCl(CO)(PR(2)[NC(4)H(3)C(O)Me-2])(2)] (R = Ph, NC(4)H(4)) react with water to give the diphosphoxane-bridged dimers [Rh(2)Cl(2)(CO)(2)(mu-PR(2)OPR(2))(2)] following cleavage of the P-N bonds to the 2-acetyl-N-pyrrolyl groups. The two dimers have been crystallographically characterized and show a number of structural differences, with the PPh(2)OPPh(2) compound possessing semibridging chloride and carbonyl ligands whereas the P(NC(4)H(4))(2)OP(NC(4)H(4))(2) compound contains only terminal chlorides and carbonyls. No evidence for cleavage of the P-N bonds involving the unfunctionalized N-pyrrolyl groups in trans-[RhCl(CO)(P[NC(4)H(4)](2)[NC(4)H(3)C(O)Me-2])(2)] was observed.

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