Geoffrey P. McQuillan

Structure and reactivity of substituted di-η5-cyclopentadienyl metal dihalides. Crystal structure of dichlorobis(η5-t-butylcyclopentadienyl) zirconium(IV)

Abstract A new approach to the synthesis of t-butylcyclopentadienyl and related anions, via the addition of methyl- or other alkyl-lithium compounds to dimethylfulvene, is reported and details are given for the preparation of (η5-t-BuCp)2ZrCl2 and (η5-t-BuCp)2TiCl2. The zirconium compound is orthorhombic, P21212, a 13.003(17), b 10.761(10), c 6.703(8) A. A crystal structure determination (R = 0.037, 980 reflections) shows that the t-butyl groups are directed away from each other on opposite sides of the molecule: this structure appears to be adopted only in molecules in which the substituent groups are too bulky to be accommodated directly above and below the MCl2 group.

Crystal and molecular structure of dichlorobis(η5-t-butylcyclopentadienyl)titanium(IV)

Abstract Dichlorobis(η 5 -t-butylcyclopentadienyl)titanium(IV), (t-BuCp) 2 TiCl 2 , crystallises in space group P 2 1 2 1 2 (orthorhombic) with a 12.862(14), b 10.709(9), c 6.602(9) A, Z = 2. The two t-butyl groups are directed away from each other on opposite sides of the molecule; the overall molecular symmetry is C 2 . The individual titanium-ring carbon atom distances are not all equal, but vary from 2.330(5) to 2.475(4) A, the distortion from an exactly symmetric conformation being in a direction which increases the separation between the titanium atom and the carbon atom carrying the t-butyl substituent group.

Vibration spectrum, structure and complex-forming reactions of “Imidobis(diphenylphosphine sulphide)”, (Ph2PS)2NH

Abstract The NH stretching vibration in (Ph2PS)2NH, “imidobis(diphenylphosphine sulphide)” cannot be detected in the i.r. spectrum at room temperature but appears as a very weak band at 3250 cm−1 at -180°C. Assignment of an i.r. band at 2640 cm−1 to an overtone of the NH bend, rather than an SH stretch, confirms the imido-structure (Ph2PS)2NH rather than the thiol structure (Ph2PS)(Ph2PSH)N for the solid compound. Skeletal P2N stretching vibrations are assigned at 920 and 781 cm−1 for (Ph2PS)2NH and at 1199 and 808 cm−1 for [(Ph2PS)N]−.Reactions of (Ph2PS)2NH with various transition metal and zinc group acceptors lead ultimately to the formation of products containing the anionic [(Ph2PS)2N]− ligand but under very mild conditions complexes containing undissociated [(Ph2PS)2NH] ligands can be isolated. The ligand field parameters 10 Dq and β are slightly but probably significantly higher for Co[(Ph2PS)2NH]2+2 than for Co[(Ph2PS)2N]2.

Isolated CH stretching frequencies, bond strengths and lengths in some mep and MeS compounds

Abstract Infrared spectra in the CH stretching region have been obtained for CHD 2 PH 2 , (CHD 2 ) 2 PH, (CHD 2 ) 3 P and (CHD 2 ) 2 S which enable small differences in CH bond strength and length to be discerned within each methyl group of each compound. Small “normal” trans effects of the lone pair of electrons are found in Me 3 P and Me 2 S, compared with essentially zero ones in Me 2 PH and MeSH and a small “abnormal” effect (CH trans to lone pair stronger than CH trans to PH) in MePH 2 . Ab initio calculations of r e CH using the 4-31G basis set have been made for the above molecules and for Me 3 N. For the latter, the difference in r e CH within the methyl group is calculated to be 0.015 A, in excellent agreement with the predicted Δ r O CH value of 0.016 A. The smaller differences Δ r O CH in the MeP and MeS compounds are not well reproduced, r e CH 1p is consistently smaller than or equal to r e CH H or Me , in agreement with the negative trans effect found in MePH 2 , but the influence of Me substitution in reversing this is not predicted.

Crystal structure and coordination chemistry of (2-carbomethoxyethyl)iododiphenylstannane, Iph2SnCh2Ch2CO2Me

Abstract The crystal structure of IPh2SnCH2CH2Co2Me: C16H17IO2Sn (10; X = I) has been determined; the tin atom adopts a distorted trigonal bipyramidal geometry, with iodine and the internal carbonyl oxygen in axial sites. The chelated structure of 10 (X = I) [v(CO) 1684 cm−1] persists in such solvents as dichloromethane, chloroform, tetrahydrofuran and acetonitrile. Pyridine is able to compete with the intramolecular ester coordination in CH2Cl2 solution with the formation of unchelated IPh2Sn(py)CH2CH2CO2Me (11) [v(CO) 1734 cm−1]; the formation constant of 11 is 0.07 ± 0.01 1 mol−1 at 25°C.

Structures of tetracarbonyl(di-2-pyridylamine)chromium(0), -molybdenum(0) and -tungsten(0) crystallographic and spectroscopic evidence for an intermolecular NH----OC hydrogen bond

Abstract The complexes [M(CO)4·dipyam] [M = Cr, Mo, W; dipyam: di-2-pyridylamine, (C5H4N)2NH] are triclinic, space group P 1 , Z = 2. The molybdenum and tungsten complexes are isostructual. Cell dimensions (Cr, Mo, W) are a = 8.436(2), 6.919(1), 6.951(1); b = 8.893(2), 13,385(2), 13.352(2); c = 10.382(2), 8.504(1), 8.455(1) A; α = 88.8(1), 81.0(1), 81.0(1); β = 82.1(1), 68.3(1), 68.3(1); γ = 65.4(1), 86.1(1), 85.9(1)°. A single crystal structure determination for [Mo(CO)4·dipyam] (1266 reflections, R = 0.062) shows the complex to be octahedral and mononuclear, but with an intermolecular contact between the uncoordinated NH group and a carbonyl oxygen atom in an adjoining molecule which is close enough(H---O calc., 2.23 A) to satisfy the usual criterion for a weak hydrogen bond. The NH and B2 carbonyl stretching frequencies in the crystal are 55 cm−1 and about 40 cm−1, respectively, lower than in solution, consistent with the proposed hydrogen-bonded structure. The tungsten complex is similar with perhaps a marginally stronger hydrogen bond, but the infrared and structural data for [Cr(CO)4·dipyam] indicate that in this case hydrogen-bonding is minimal or non-existent.

Isolated CH stretching frequencies, methyl group geometry and dissociation energies in dimethyl zinc, cadmium and mercury

Infrared spectra in the CH stretching region are reported for CHD2 substituted zinc, cadmium and mercury dimethyl. The isolated CH stretching frequencies derived therefrom are used to predict values of r0CH on which are based new geometries for these molecules. An earlier correlation between νisCH and HCH appears to break down in these compounds. A new correlation with D(MCH3) is apparent in both MMe2 and MMe4, compounds, which favours a value for D(SiCH3) near 78 kcal mol−1. Estimates of the unperturbed positions of νsCH3 are made.

Diphosphine derivatives—I. The vibrational spectrum of tetramethyldiphosphine disulphide (tmps) and of tmps-d12 and tmps-13C4

Abstract The i.r. and Raman spectra of tetramethyldiphosphine disulphide (tmps) and of tmps-d 12 and tmps- 13 C 4 are reported and the assignment of the skeletal modes is discussed. Raman polarization data confirm previous assignments for the PS and PP stretching modes and the symmetric PPS bend is assigned at Δν = 170 cm −1 . There is no evidence of trans-gauche or trans-cis isomerism in solution: it is estimated that the molecule remains at least 99.5% in or very close to the trans form in chloroform or methylene chloride. The small dipole moment in benzene solution most probably arises from small distortions of the trans -structure, rather than trans-gauche isomerism. It has been suggested that the solid compound contains two significantly different types of tmps molecule but there is no evidence of this in the solid vibrational spectrum. Interactions between the skeletal and internal methyl vibrations are significant and are illustrated by the appreciable frequency shifts which occur in many of the skeletal modes in the deuterated compound.

Infrared spectra of MeTiCl3 species, methyl group geometry and a force field

Abstract Infrared spectra have been recorded between 4000 and 200 cm −1 from 12 CH 3 TiCl 3 in the gas and solid, and 12 CD 3 TiCl 3 in the gas phase. 13 CH 3 TiCl 3 and CHD 2 TiCl 3 have been studied in the gas phase down to 450 cm − . All fundamentals, apart from the torsion and δTiCl modes, are securely located. The δ as CH 3 and ϱCH 3 frequencies are abnormally low, the remaining vibrations of the methyl group being normal for an organometallic compound. The νCH and νCD frequencies are consistent with the unexceptional methyl geometry of a recent electron diffraction investigation, with ∠HCH≈ 110.8°. They show no sign of an “agostic” interaction in the solid state. A force field having five off-diagonal constants has been determined.

Complexes of acridine N-oxide with some transition metal and group IIb metal halides, thiocyanates and nitrates

Acridine N-oxide forms complexes having 1:1 or 1:2 metal: ligand stoichiometry with Mn(II), Co(II), Ni(II), Zn(II) or Hg(II) halides, thiocyanates or nitrates. Unlike corresponding pyridine N-oxide or quinoline N-oxide systems, no products were obtained having more than two acridine N-oxide molecules per metal ion, or containing additional co-ordinated water or solvent molecules. The preference of acridine N- oxide for 1:1 or 1:2 complexes appears to be the result of insolubility, rather than steric or electronic, effects. In tetrahedral complexes (e.g. [CoCl2(aco)2]), metal-oxygen and metal-chlorine stretching vibrations are assigned between 300–400 cm−1. Octahedral complexes (e.g. [CoCl2(aco)]) have ligand-bridged structures and their i.r. spectra contain no identifiable metal-ligand bands above 300 cm−1. It is suggested that a vibration at 1085 cm−1 in the i.r. spectrum of acridine N-oxide contains a substantial contribution from the NO stretching co-ordinate.