Colin Overton

Binuclear 2,2′-bipyrimidine complexes derived from chromium, molybdenum and tungsten carbonyls

Abstract Reaction of 2,2′-bipyrimidine (bpym) with [Mo(CO)4(diene)] gives [Mo(CO)4(bpym)], which will react with [M(CO)4(diene)] to form [MoM(CO)8(bpym)] (M = Cr, Mo, W). The bipyrimidine complexes are characterised by microanalysis and spectroscopy (IR, 1H and 13C NMR, UV/vis). Reduction of [Mo2(CO)8(bpym)] produces an anion in which the unpaired electron is localised on the bridging bpym ligand.

Substituted 2,2′-bipyridines as ligands. preparation and characterization of 4,4′-disubstituted 2,2′-bipyridine derivatives of the hexacarbonyls of chromium, molybdenum and tungsten

The preparation of cis-[M(CO)4(biL)] (M = Cr, Mo, W; biL is 4,4′X2-2,2′-Bipyridine; X = NMe2, NH2, OMe, CMe3, Me, H, Ph, CHCHPh, Cl, CO2H, CO2Me, NO2) is reported. The ligands and complexes are characterized by spectroscopy (IR, electronic absorption and emission, NMR (1H, 13C, 15N, 95Mo)) and microanalysis. The variations observed in the spectroscopic properties of these complexes are strongly correlated with electronic substitutent parameters of the group X. This is most apparent in the lowest energy (visible) absoprtion which changes by ca. 0.8 eV between the extremes of donor and of acceptor substituent used.

Electronic spectra and electrochemistry of disubstituted 2,2′-bipyridinetetracarbonylmolybdenum complexes. Solvent and substituent effects

Abstract Electronic absorption spectra of cis -[Mo(CO) 4 ( n,n ′-X 2 -bipy)] ( n = 4, X = NMe 2 , NH 2 , OMe, CMe 3 , Me, H, Ph, CH:CHPh, CO 2 H, Cl, CO 2 Me, NO; n =5, X = Me, CO 2 H) have been measured at ambient temperature in a variety of solvents of different polarity. Emission spectra from glasses containing the complexes at 77 K have also been measured. The influence of the substituent X on the spectroscopic properties is correlated with the Hammett parameters, σ p (X) and σ p + (X). The effect of solvent is correlated with the Taft-Kamlet parameter, π ★ , indicating charge redistribution along the permanent dipole axis of the complex. The oxidation and reduction potentials in solution are simply related to the electronic effect of the substituent group, X, and are relatively independent of the solvent. The influence of the metal on these properties is not significant.

Solvent influences on the infrared absorption and nuclear magnetic resonance spectra of 4,4-disubstituted-2,2′-bipyridinetetracarbonylmolybdenum complexes

Abstract Proton and carbon NMR spectra of both 4,4′-X2-bipy and cis-[Mo(CO)4(4,4′-X2-bipy)] (X = OMe, CMe3, Me, H, Cl, CO2 Me) have been recorded in solvents (chloroform, dimethyl sulphoxide) of different polarity. The measurements show that the influence of the solvent on the chemical shifts of the bipyridine ring increases significantly as a result of coordination to the metal. Changes in solvent polarity may discriminate between different carbon atoms and the protons attached to them. Measurements of infrared spectra (2100–1700 cm−1) of the complexes (X = OMe, CMe3, Me, CO2Me, NO2) in solution indicate that there is a preferential interaction between the solvent and the equatorial CO ligands which are trans to 4,4′-X2-bipy.

Molybdenum carbonyl complexes of binucleating pyridine-based ligands

Abstract Reaction of [Mo(CO) 4 (diene)] with 4,4′-bipyridine (44′B), trans -1,2-bis(2-pyridyl)ethene (2-bpe) and trans -1,2- bis (4-pyridyl)-ethene (4-bpe) gives polymeric [Mo(CO) 4 (44′B)] n , mononuclear cis -[Mo(CO) 4 (2-bpe) 2 ] and binuclear [Mo(CO) 4 (4-bpe)] 2 respectively. Reaction of the same ligands with [Mo(CO) 4 (bpy)] (bpy is 2,2′-bipyridine) produces the bridged binuclear complexes [{Mo(CO) 3 (bpy)} 2 (44′B)] and [{Mo(CO) 3 (bpy)} 2 (4-bpe)]. Products are characterised by microanalysis and spectroscopy (IR, 1 H NMR, UV/vis). Reduction of [{Mo(CO) 3 (bpy)} 2 (44′B)] produces an anion in which the unpaired electron is localised on the chelating bpy ligand.

Chemistry of cis-bis(2,2′-bipyridine)dicarbonyl-molybdenum(0) and -tungsten(0). Substitution reactions with phosphorus donor ligands and with lsocyanides

Nucleophilic substitution reactions of cis-[M(CO)2(bipy)2](M = Mo or W; bipy = 2,2′-bipyridine) by various unidentate (PR3; R = Ph, Bun, or OMe) and bidentate (Ph2PCH2CH2PPh2= dppe) phosphorus and carbon (CNR; R = Et or p-tolyl) donor ligands, L, result in displacement of bipy to produce cis,trans-[Mo(CO)2L2(bipy)](L = PR3), cis,cis-[M(CO)2L2(bipy)][M = Mo, L2=(CNEt)2 or dppe; M = W, L = CNEt], cis-[M(CO)2L4](M = Mo or W; L = CNC6H4Me-p), and fac-[Mo(CO)3L(bipy)](L = PPh3) depending on the ligand L, temperature, and solvent. Trifluorophosphine reacts with cis-[Mo(CO)2(bipy)2] to displace CO and form cis-[Mo(PF3)2(bipy)2]. Substitution in [M(CO)4(bipy)] by isocyanides gives fac-[M(CO)3(CNR)(bipy)](M = Cr; R = Et or p-tolyl; M = Mo, R = Et) or cis-[Mo(CO)4(CNR)2](R =p-tolyl). The products are characterised by microanalysis and by i.r., 1H and 31P n.m.r. electronic, and mass spectroscopy. It is suggested that the formation of cis,trans-[Mo(CO)2L2(bipy)] may involve a trigonal biprismatic intermediate structure which allows reorganisation to occur simply. The acceptor strength of L in [Mo(CO)2L2(bipy)] indicated by i.r. [ν(CO)], 1H n.m.r. (bipy ring chemical shifts), and visible (Mo → bipy dπ*) spectra, decreases in the order CO > P(OMe)3 > CNEt > PBu3 > bipy, which does not reflect geometrical differences in the disposition of these ligands.

Oxidation and reduction of cis-bis(2,2′-bipyridine)dicarbonylmolybdenum(0) and -tungsten(0). Preparation of bis(2,2′-bipyridine)-dicarbonyl(solvent)molybdenum(II) bis(tetrafluoroborate) salts and their reaction with isocyanides

Oxidation of cis-[M(CO)2(bipy)2](M = Mo or W; bipy = 2,2′-bipyridine) with silver(I) tetrafluoroborate in solution produces red-brown, diamagnetic [Mo2(CO)4(bipy)4][BF4]2 or orange cis-[W(CO)2(bipy)2][BF4]. [Mo2(CO)4(bipy)4][BF4]2 dissociates in acetone solution to form green, paramagnetic trans-[Mo(CO)2(bipy)2][BF4]. Addition of one equivalent of silver(I) ion to the metal(I) cations in solution produces cis-[Mo(CO)2(bipy)2(solvent)][BF4]2(solvent = MeCN, Me2CO, or H2O) or cis-[W(CO)2(bipy)2][BF4]2. Oxidation of cis-[Mo(CO)2(phen)2](phen = 1,10-phenanthroline) with Ag[BF4](two equivalents) in acetonitrile produces cis-[Mo(CO)2(phen)2(NCMe)][BF4]2. cis-[Mo(CO)2(bipy)2] reacts with [NO][PF6] to form [Mo(CO)(NO)(bipy)2][PF6]. Addition of isocyanides, RNC (R = Et or C6H4Me-p), to cis-[Mo(CO)2(bipy)2(NCMe)][BF4]2 in acetonitrile solution at room temperature produces, successively, [Mo(CNR)3(bipy)2][BF4]2 and [Mo(CNR)5(bipy)][BF4]2. The new complexes have been characterised by microanalysis, spectroscopy [i.r., 1H, and 13C n.m.r., mass (fast atom bombardment), electronic absorption], conductivity measurements, and electrochemistry in solution. Reduction of cis-[Mo(CO)2(bipy)2] with sodium amalgam in tetrahydrofuran solution produces paramagnetic cis-[Mo(CO)2(bipy)2]˙–. Reaction of CNEt with [{Mo(CO)4Cl2}2] in dichloromethane, followed by anion exchange with [NH4][PF6] produces [Mo(CNEt)7][PF6]2.

Substitution reactions of cis-bis(2,2′-bipyridine)dicarbonyl(solvent)molybdenum(II) and cis-bis(2,2′-bipyridine)dicarbonyltungsten(II) salts with uni-, bi-, and ter-dentate tertiary phosphines, trimethyl phosphite, nitric oxide, and 2,2′-bipyridine

Reaction of cis-[Mo(CO)2(bipy)2(NCMe)][BF4]2(bipy = 2,2′-bipyridine) with PPh3 and PBun3 substitutes the solvent to produce [Mo(CO)2(bipy)2(PR3)][BF4]2(R = Ph or Bun) under mild conditions. Oxidation of cis-[Mo(CO)2(bipy)2] with Ag[BF4] in trimethyl phosphite at room temperature gives [Mo(CO)2(bipy)2{P(OMe)3}][BF4]2. Under similar conditions, further substitution of one carbonyl ligand, to give [Mo(CO)(bipy)2L2][BF4]2[L = PEt3 or P(OMe)3], or both carbonyl ligands to give [Mo(NO)2(bipy)2][BF4]2 or [Mo(bipy)3][BF4]2 may occur. Reaction of cis-[W(CO)2(bipy)2][BF4]2 with the same phosphorus donor ligands results in the substitution of bipy to form cis-[W(CO)2(bipy)L2][BF4]2[L = PPh3 or P(OMe)3]; reaction with bis(diphenylphosphino)methane (dppm) or 1,2-bis(diphenylphosphino)ethane (dppe) produces [WF(CO)2(bipy)(L–L)][BF4](L–L = dppm or dppe). Reaction of [Mo(CO)2(bipy)2(NCMe)][BF4]2 with dppe produces [Mo(CO)(bipy)2(dppe)][BF4]2. With bis(2-diphenylphosphinoethyl)phenylphosphine (bdpp), cis[W(CO)2(bipy)2][BF4]2 forms [W(CO)2(bipy)(bdpp)][BF4]2 in high yield. The new complexes have been characterised by microanalysis, spectroscopy (i.r., 1H, 13C, 19F, 31P n.m.r., electronic absorption), and conductivity measurements. [Mo(NO)2(bipy)2][BF4]2 reacts with Na[S2CNEt2] to give [Mo(NO)2(S2CNEt2)2].

Redox and isocyanide substitution chemistry of bis(2,2′-bipyridine) derivatives of molybdenum and tungsten carbonyl

Abstract Redox reactions of cis -[Mo(CO) 2 (bpy) 2 ] (bpy is 2,2′-bipyridine) produce [Mo(CO) 2 (bpy) 2 ] z ( z  ±1, +2), which rea