Anthony G. Osborne

[1] Ferrocenophanes. synthesis and spectroscopic properties of [1] ferrocenophanes with group IV and V elements as bridge atoms

Abstract The [1]ferrocenophanes, 1,1′-ferrocenediyldiphenylsilane, bis(1,1′-ferrocenediyl)silane, 1,1′-ferrocenediyldiphenylgermane and 1,1′-ferrocenediylphenylphosphine have been prepared by the reaction of 1,1′dilithioferrocenebis N , N , N′ , N′ -tetramethylethylenediamine) with dichlorodiphenylsilane, tetrachlorosilane, dichlorodiphenylgermane and P , P -dichlorophenylphosphine, respectively. Similar reactions with dichlorodimethyltin or dichlorodiphenyltin yielded only polymeric products. The Group IV [1]ferrocenophanes are red, air-stable, crystalline solids; the phosphorus compound is red-purple and is moderately air-sensitive. The spectroscopic properties of the compounds, which are consistent with ring-tilted structures, are reported and discussed.

Ring-tilted ferrocenophanes. the crystal and molecular structures of (1,1′-ferrocenediyl)diphenylgermane and (1,1′-ferrocenediyl)phenylphosphine

Abstract The structures of (1,1′-ferrocenediyl)diphenylgermane (B) and (1,1′-ferrocenediyl)phenylphosphine (C) have been determined from a three-dimensional X-ray analysis using diffractometer data. Crystals of compound B are orthorhombic, space group, Pnma , with Z = 4 in a unit cell of dimensions a 14.867(9), b 12.522(7) and c 9.373(6) A. Full matrix least-squares refinement has given a final R -factor of 0.069 for 956 reflections for which I > 3 σ ( I ). The structure is isomorphous with (1,1′-ferrocenediyl)diphenylsilane [3]. The molecule has crystallographic m symmetry, with atoms Fe and Ge lying in the mirror plane, which bisects the two phenyl groups. The planar cyclopentadienyl rings are bridged by a single Ge atom and are inclined at an angle of 16.6° to one another. The bridge angle, C(1)GeC(1′) is 93.6° and the shortest inter-ring distance, C(1)C(1′), is 2.86 A. the exocyclic C(1)Ge bond makes an angle of 38° with the plane of the cyclopentadienyl ring. Crystals of compound C are orthorhombic, space group Pbca , with Z = 8 in a unit cell of dimensions a 27.130(10), b 12.701(8) and c 7.380(5) A. Full matrix least-squares refinement converged at R = 0.059 for 996 reflections for which I > 3 σ ( I ). The molecule has only an approximate mirror plane, close to which lie atoms Fe, P, C(6) and C(9). The planar cyclopentadienyl rings are bridged by a single P atom and are inclined at an angle of 26.7° to one another. The bridge angle C(1)PC(1′) is 90.6° and the shortest inter-ring distance, C(1)C(1′), is 2.62 A. The exocyclic C(1)P and C(1′)P bonds make angles of 32° and 33° to their respective cyclopentadienyl rings.

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 2. Rhenium carbonyl halide complexes, fac-[ReX(CO)3(terpy)](X = Cl, Br or I): NMR studies of their solution dynamics, synthesis of cis-[ReBr(CO)2(terpy)] and the crystal structure of [ReBr(CO)3(terpy)]

Under mild conditions pentacarbonylhalogenorhenium(I) complexes react with 2,2′:6′,2″-terpyridine (terpy) to form stable octahedral tricarbonyl complexes fac-[ReX(CO)3(terpy)](X = Cl, Br or I) in which the terpyridine acts as a bidentate chelate ligand. Under more severe reaction conditions fac-[ReBr(CO)3(terpy)] can be converted to cis-[ReBr(CO)2(terpy)]. In solution the tricarbonyl complexes are fluxional with the terpyridine oscillating between equivalent bidentate bonding modes. At low temperatures rotation of the unco-ordinated pyridine ring is restricted and in CD2Cl2 solution two preferred rotamers exist in approximately equal abundances. Rotational energy barriers have been estimated for the X = Cl and I complexes. The X-ray crystal structure of fac-[ReBr(CO)3(terpy)] confirms the bidentate chelate bonding of terpy with a N–Re–N angle of 74.3°. The pendant pyridine ring is inclined at an angle of 52.9° to the adjacent co-ordinated ring and the unco-ordinated nitrogen is directed towards the axial carbonyl and trans to Br.

Synthetic and structural studies on some [3]ferrocenophanes with trichalcogen bridges. Crystal and molecular structure of 1,3-dithia-2-selena-[3]ferrocenophane

Abstract A series of [3]ferrocenophanes with the symmetrical trichalcogen chains: Se3, SSeS, STeS, SeSSe, SeTeSe, as bridging groups has been synthesized. In solution these compounds are fluxional by a bridge-reversal process. The crystal structure of 1,3-dithia-2-selena-[3]ferrocenophane, which is isomorphous with that of the known 1,2,3-trithia-[3]ferrocenophane, has been determined to assess the effect on molecular geometry of replacement of the central S by Se. Expansion of the bridgehead bonds from SS 2.049(4) A to SSe 2.195(3) A is compensated by a contraction of the bridgehead valence angle from SSS 103.9(2)° to SSeS 100.5(1)°, and by an outward displacement of the S atoms by 0.04 A from the cyclopentadienyl ring planes. Intramolecular repulsions involving Se and adjacent non-bonded ring carbon atoms lead to enhanced asymmetry of the exocyclic CCS valence angles, which have been values of 123.4(4)° and 128.2(4)° compared with 124.0(9)° and 127.1(10)° in the trithia compound. Crystals of the title compound have space group P21/c with a = 9.683(3), b = 9.364(3), c = 11.609(4) A, β = 95.61(2)°, and Z = 4. Least-squares refinement gave R = 0.038 for 1408 unique observed reflections whose intensities were measured by counter diffractometry with Mo-Kα radiation.

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 4. cis-[M(C6F5)2(terpy)](M = Pd or Pt): nuclear magnetic resonance studies of their solution dynamics and crystal structure of cis-[Pd(C6F5)2(terpy)]

2,2′:6′,2″-Terpyridine reacted with trans-[M(C6F5)2(diox)2](M = Pd or Pt, diox = 1,4-dioxane) to form the square-planar complexes cis-[M(C6F5)2(terpy)] in which the terpyridine acts as a bidentate chelate ligand. In solution these complexes are fluxional with the terpyridine oscillating between equivalent bidentate modes by a mechanism consisting of a ‘tick-tock’ twist of the metal moiety through an angle equal to the N–M–N angle of the metal centre. Rates of this fluxion were measured by NMR spectroscopy from the exchange effects on the 1H signals of the aromatic hydrogens and in the 19F signals of two C6F5 groups. The ΔG‡ values for the fluxion were ca. 71 and 94 kJ mol–1 for the complexes of PdII and PtII respectively. At below-ambient temperatures further changes in the 19F NMR spectra of both complexes were interpreted in terms of varying rates of rotation of the unco-ordinated pyridine ring, with the rates of rotation of the C6F5 rings being substantially slower at all temperatures and not separately measurable. The lowest-temperature spectra suggested the presence of a pair of degenerate rotamers each having the planes of both C6F5 rings and the unco-ordinated pyridine ring closely parallel and orthogonal to the remainder of the ligand ring system. The crystal structure of [Pd(C6F5)2(terpy)] confirms the bidentate chelate bonding of terpy with a N–Pd–N angle of 77.9°, and the pendant ring oriented at an angle of 46° to the adjacent co-ordinated ring.

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 1. Trimethylplatinum(IV) halide complexes [PtXMe3(terpy)](X = Cl, Br or I): nuclear magnetic resonance studies of their solution dynamics and crystal structure of [PtIMe3(terpy)]

2,2′:6′,2″-Terpyridine (terpy) reacts with trimethylplatinum halides [(PtXMe3)4](X = Cl, Br or I) to form stable octahedral complexes fac-[PtXMe3(terpy)](X = Cl, Br or I) in which the terpy molecule is acting as a bidentate chelate ligand. In solution the complexes are fluxional with the ligand oscillating between equivalent bidentate bonding modes by a mechanism consisting of ‘tick-tock’ twists of the metal moiety through an angle equal to the N–Pt–N angle of the octahedral centre. At below-ambient temperatures rotation of the unco-ordinated pyridine ring is severely restricted with the most favoured rotamers having the plane of the pendant pyridine ring at an angle of ca. 52° with respect to the adjacent co-ordinated pyridine ring plane. The X-ray crystal structure of [PtIMe3(terpy)] depicts the pendant pyridine N atom cis to iodine and this is the predominant species in solution at low temperatures. At above-ambient temperatures the complexes exhibit intramolecular Pt–Me exchange of axial and equatorial environments. Energy data based on accurate dynamic NMR fittings are reported for the three dynamic processes, namely pendant pyridine rotation, 1,4-Pt–N metallotopic shifts and Pt–Me scramblings.

Dynamic NMR studies of ring rotation in substituted ferrocenes and ruthenocenes

Variable temperature 1H and 13C{1H} NMR studies on 1,1′,3,3′-tetra(alkyl)-ferrocenes and -ruthenocenes (alkyl = t-pentyl,t-butyl) have provided accurate barrier energies for restricted rotations of the substituted cyclopentadienyl rings. Energies (ΔG† (298.15 K)) are in the range 40–57 kJ mol−1 and are dependent on the ‘sandwich’ metal (Fe ⋙ Ru) and alkyl substituent (t-pentyl < t-butyl). Ring rotation in 1,1′,3.3′-tetra(phenyl)ferrocene was too rapid for measurement even at 173 K. Spectral changes were analysed primarily on the basis of exchange between a mirror pair of structures having both 5-membered rings eclipsed and the alkyl substituents staggered. In the case of 1,1′,3,3′-tetra(t-butyl)ferrocene a pair of staggered ring rotamers also contributed to the observed NMR bandshape changes.

The first examples of 2,2′:6′,2″-terpyridine as a fluxional bidentate ligand

2,2′:6′,2″-Terpyridine (terpy) forms octahedral complexes fac-[ReBr(CO)3(terpy)], cis-[W(CO)4(terpy)] and fac-[PtClMe3(terpy)] in which the ligand oscillates between equivalent bidentate forms by a mechanism involving a ‘tick-tock’ twist of the metal moiety through an angle equal to the N–M–N angle of the octahedral centre and involving a seven-coordinate metal intermediate.

Synthesis and dynamic NMR studies of fluxionality in palladium(II) and platinum(II) complexes of 2,4,6,-tris(2-pyridyl)-1,3,5-triazine (TPT) and 2,4,6-tris(2-pyridyl)-pyrimidine (TPP)

Complexes of general formulae cis-[M(C6F4CF3)2L] (M = PdII, PtII; L = 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPT) and 2,4,6-tris(2-pyridyl)-pyrimidine (TPP) were isolated as air-stable solids. In all cases cis square-planar complexes were formed with the nitrogen ligands acting as bidentate chelates towards each metal moiety. The complexes exhibited various modes of fluxionality in solution, namely 1,4-metallotropic shifts, a new ‘metal hurdling’ fluxion and, at below-ambient temperatures, restricted rotation of the pendant pyridyl ring adjacent to the metal chelate ring. Dynamic NMR experiments (one-dimensional bandshape analysis and two-dimensional EXSY experiments) provided activation energy data for these processes. Gibbs free energy values (ΔG≠ (298.15 K)) were in the ranges 74–113 (metal hurdling). 69–118 (metal 1,4-shifts) and 37–43 (pendant pyridyl rotations) kJ mol−1. Energies of any of these fluxions were considerably higher in the PtII complexes than in the PdII complexes. To aid understanding of the low temperature fluxionality of the TPT complexes, the complex [Pd(C6F4CF3)2(mstd)] (mstd = meso-stilbenediamine) was synthesised. At low temperatures, C6F4CF3 ring rotations and five-membered ring puckering in this complex were arrested, ΔG≠ (208K) for the latter process being 42.8 kJ mol−1.

The syntheses, structures, and stereodynamics of [3]ferrocenophane complexes: I. Group 6 metal tetracarbonyl complexes, cis-[M(CO)4{(C5H4ECH3)2Fe}]. (M = Cr, Mo, W; E = S or Se). Crystal structure of 1,1′-bis(methylseleno)ferrocene tetracarbonyltungsten

Abstract The complexes cis-[M(CO)4{(C5H4ECH3)2Fe}] (M = Cr, Mo or W; E = S or Se) have been synthesised. Pyramidal inversion of the coordinated S or Se atoms was arrested in most cases at low temperatures (∼ −80°C), when the DL forms of the complexes predominated (⩾ 78%). At higher temperatures combined 1D and 2D-EXSY NMR studies led to energies (ΔG‡(298 K) values) for chalcogen inversion in the range 31–50 kJ mol−1. Fairly large ΔS‡ values for these processes were attributed to the rapid reversal of the EM(CO)4E portion of the ferrocenophane ring. The crystal structure of 1,1′-bis(methylseleno)ferrocene tetracarbonyltungsten has been determined. The crystals have space group P21/a with a 17.580(3), b 9.665(1), c 11.059(1) A, β 107.33(1)° and Z = 4. Least-squares refinement gave R = 0.031 for 2369 independent significant reflections. The WSe bond lengths are 2.674(4) and 2.692(4) A, and the SeMe groups adopt a DL relationship. The SeWSe bond angle is 86.3° and the non-bonded SeSe separation 3.67 A. The cyclopentadienyl rings adopt an eclipsed conformation with the ring planes parallel.