Kandasamy G. Moodley

Stabilisation of [Fe2(CO)9] and [Ru2(CO)9] bu substitution with bridging diphosphorus ligands

Abstract Reaction of [Fe 2 (CO) 9 ] with a half molar amount of R 2 PYPR 2 (Y = CH 2 , R = Ph, Me, OMe or OPr i ; Y = N(Et), R = OPh, OMe or OCH 2 ; Y = N(Me), R = OPr i or OEt) leads to the ready formation of a product which on irradiation with ultraviolet light rapidly decarbonylates to the heptacarbonyl derivative [Fe 2 (μ-CO)(CO) 6 {μ-R 2 PYPR 2 }]. Treatment of the latter with a slight excess of the appropriate ligand results, under photochemical conditions, in the formation of the dinuclear pentacarbonyl complex [Fe 2 (μ-CO)(C)) 4 {μ-R 2 PYPR 2 } 2 ] but under thermal conditions in the formation of the mononuclear species [Fe(CO) 3 {R 2 PYPR 2 }]. Reaction of [Ru 3 (CO) 12 ] with an equimolar amount of (RO) 2 PN(R′)P(OR) 2 (R′ = Me, R = Pr i or Et; R′ = Et, R = Ph or Me) under either thermal or photochemical conditions produces [Ru 3 (CO) 10 {μ-(RO) 2 PN(OR) 2 }] which reacts further with excess (RO) 2 PN(R′)P(OR) 2 on irradiation with ultraviolet light to afford the dinuclear compound [Ru 2 (μ-CO)(CO 4 {μ-(RO) 2 PN(R′)P(OR) 2 } 2 ]. The molecular structure of [Ru 2 (μ-CO)(CO) 4 {μ-(MeO) 2 PN(Et)P(OMe) 2 } 2 ], which has been determined by X-ray crystallography, is described.

Reaction of triruthenium dodecacarbonyl with bis(dimethylphosphino)methane, bis(diphenylphosphino)methane and bis(diphenylphosphino)-ethylamine under photochemical conditions

Abstract The photochemical reactions of [Ru 3 (CO) 12 ] with the diphosphorus ligands Me 2 PCH 2 PME 2 , Ph 2 PCH 2 PPh 2 and Ph 2 PN(Et)PPh 2 have been found to give tri-, di- or mono-nuclear products, depending on the reaction conditions and the ligand involved. Products isolated include [Ru 3 (CO) 10 [μ-R 2 PYPR 2 ] (Y = CH 2 , R = Me or Ph; Y = N(Et), R = Ph), [Ru 3 (CO) 8 [μ-R 2 PYPR 2 ] 2 ] (Y = CH 2 , R = Me or Ph), [Ru 3 (CO) 6 [μ-R 2 PYPR 2 ] 3 ] (Y = CH 2 , R = Me or Ph), [Ru 2 (μ-CO)(CO) 4 [μ-Ph 2 PCH 2 PPh 2 ] 2 ] and [Ru(CO) 3 [Ph 2 PN(Et)PPh 2 ]. An X-ray crystallographic study has revealed that the diphosphazane ligand in [Ru 3 (CO) 10 [η-Ph 2 PN(Et)PPh 2 ] is coordinated equatorially and that the Ru-Ru edge which it bridges is ca. 0.06 A shorter than the average of the other two edges.

The tungsten-tungsten triple bondXVI. Bis(cyclopentadienyl)- and bis(indenyl)tetradimethylamidoditungsten (WW) ☆

Abstract From the reaction between 1,2-W2Cl2(NMe2)4 and NaCp (Cp = C5H5) (two equiv.) in toluene, a yellow-orange, hydrocarbon-soluble, crystalline solid of formula W2Cp2(NMe2)4 has been obtained. NMR data are consistent with a gauche 1,2- W2R2(NMe2)4 molecule having a WW triple bond and restricted rotations about the WN bonds. The NMR data, however, do not uniquely define the nature of the CpW bonding beyond the fact that there are five time-averaged equivalent carbon and hydrogen atoms. No crystals suitable for an X-ray study were obtained. The related reaction involving 1,2-W2Cl2(NMe2)4 and LiC9H7 (C9H7 = indenyl) (two equiv.) gave an orange, hydrocarbon-soluble, crystalline compound. The NMR data are indicative of a gauche 1,2- W2R2(NMe2)4 molecule in solution having a virtual C2 axis of symmetry and restricted rotations about the WN bonds. An X-ray study rev ealed the presence of the gauche rotamer and that the indenyl-metal bonding was η3-C9H7. Pertinent bond distances (A) and angles (°) for 1,2-W2(η3-C9H7)2(NMe2)4 are WW = 2.334(1), WN = 1.96(1) (av.), and W-η3-C3(indenyl) = 2.36(1)–2.54(1), WWN = 102(1) (av.) and WWC(η3-C3(indenyl)) = 91–117°. The reaction between 1,2-W2Cp2(NMe2)4 and EtCOOCOEt (> four equiv.) proceeds in hydrocarbon solvents to give the compound W2Cp2(NMe2)(O2CEt)3 and Me2NCOEt (three equiv.) in contrast to other 1,2-W2R2(NMe2)4 compounds which yield either W2(O2CEt)4 when R contains β-hydrogen atoms or W2R2(O2CEt)4 compounds. The molecular structure of W2Cp2(NMe2)(O2CEt)3 can be viewed as two fused four-legged piano-stools sharing an edge, μ-NMe2 and μ-η1-O2CEt, with a pair of bridging O 2CEt ligands spanning a WW bond of distance 2.78 A. The Cp ligands form W-η5-C5H5 bonds roughly trans to the WW axis.

Protonation of a series of diphosphazane- and diphosphine-bridged derivatives of iron and ruthenium: dependence of the nature of the hydride ligand on the metal and the bridging diphosphorus ligand

Abstract Protonation of the dinuclear compounds [M 2 (μ-CO)(CO) 4 (μ-R 2 PYPR 2 ) 2 ] by HBF 4 or HPF 6 leads to the formation of crystalline cationic hydrido products [M 2 H(CO) 5 (μ-R 2 PYPR 2 ) 2 ]X and [M 2 (μ-H)(μ-CO)(CO) 4 (μ-R 2 PYPR 2 ) 2 ]X (X = BF 4 or PF 6 ) in which the hydride ligand is terminal for M = Ru, Y = N(Et) and R = OMe or OPr i and bridging for M = Fe, Y = CH 2 and R = Me or Ph, for M = Fe, Y = N(Et) and R = OMe, OEt, OPr i or OPh and for M = Ru, Y = CH 2 and R = Ph; the fluxional behaviour of [Ru 2 H(CO) 5 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ] + (R = Me or Pr i ) in solution is described.

The tungsten-tungsten triple bond18. Bridging and terminal allyl ligands in complexes of the formula W2(R)2(NMe2)4, where R C3H5 and C4H7

Abstract The reaction between RMgCl (two equivalents) and 1,2-W2Cl2(NMe2)4 in hydrocarbon solvents affords the compounds W2R2(NMe2)4, where R = allyl and 1− and 2-methyl-allyl. In the solid state the molecular structure of W2(C3H5)2(NMe2)4 has C2 symmetry with bridging allyl ligands and terminal WNMe2 ligands. The WW distance 2.480(1) A and the CC distances, 1.47(1) A, imply an extensive mixing of the allyl π-MOs with the WW π-MOs, and this is supported by an MO calculation on the molecule W2(C3H5)2(NH2)4 employing the method of Fenske and Hall. The most notable interaction is the ability of the (WW)6+ centre to donate to the allyl π*-MO (π3). This interaction is largely responsible for the long WW distance, as well as the long CC distances, in the allyl ligand. The structure of the 2-methyl-allyl derivative W2(C4H7)2(NMe2)4 in the solid state reveals a gauche-W2C2N4 core with WW = 2.286(1) A and WC = 2.18(1) A, typical of WW and WC triple and single bonds, respectively. In solution (toluene-d8) 1H and 13C NMR spectra over a temperature range −80°C to +60°C indicate that both anti- and gauche- W2C2N4 rotamers are present for the 2-methyl-allyl derivative. In addition, there is a facile fluxional process that equilibrates both ends of the 2-methyl-allyl ligand on the NMR time-scale. This process leads to a coalescence at 100°C and is believed to take place via an η3-bound intermediate. The 1-methyl-allyl derivative also binds in an η1 fashion in solution and temperature-dependent rotations about the WN, WC and CC bonds are frozen out at low temperatures. The spectra of the allyl compound W2(C3H5)2(NMe2)4 revealed the presence of two isomers in solution—one of which can be readily reconciled with the presence of the bridging isomer found in the solid state while the other is proposed to be W2(η3-C3H5)2(NMe2)4. The compound W2R2(NMe2)4 where R = 2,4-dimethyl- pentadiene was similarly prepared and displayed dynamic NMR behaviour explainable in terms of facile η1 = η3 interconversions.

Synthesis and protonation of mixed diphosphorus ligand-bridged derivatives of di-iron nonacarbonyl

Abstract Reaction of the di-iron heptacarbonyl compounds [Fe2(μ-CO)(CO)6(μ-R2PCH2PR2)2] (R = Me or Ph) with a range of diphosphorus or diarsenic ligands under photochemical conditions affords the ligand-bridged pentacarbonyl derivatives [Fe2(μ-CO)(CO)4(μ-Me2PCH2PMe2)(μ-L-L)] [L-L = (MeO)2PN(Et)P(OMe)2 or (EtO)2PN(Me) P(OEt)2] and [Fe2(μ-CO)(CO)4(μ-Ph2PCH2PPh2)(μ-L-L)] [L-L = Me2PCH2PMe2, Ph2PN(Et)PPh2, Ph2AsCH2AsPh2, (MeO)2PN(Et)P(OMe)2 and (EtO)2PN(Me)P(OEt)2] in good yield. Treatment of these mixed ligand-bridged complexes with the protic acids HBF4 · Et2O or CF3COOH leads exclusively to the formation of the hydride-bridged species [Fe2(μ-H)(μ-CO)(CO)4(μ-R2PCH2PR2)(μ-L-L)]+ isolated as the tetrafluoroborate salts. Hydride-bridged products are also obtained by protonation of [Fe2(μ-CO)(CO)4{μ-(R′O)2PN(R″)P(OR′)2}2] (R″ = Me, R′ = Et; R″ = Et, R′ = Me, Pri or Ph) and [Fe2(μ-CO)(CO)4(μ-R2PCH2PR2)2] (R = Me or Ph), but whereas the diphosphazane-bridged species [Fe2(μ-H)(μ-CO)(CO)4{μ-(R′O)2PN(R″)P(OR′)2}2]+ are only stable to deprotonation in the presence of excess acid, the ditertiary phosphine-bridged species [Fe2(μ-H)(μ-CO)(CO)4(μ-R2PCH2PR2)2]+ can only be deprotonated by strong bases such as NaBH4. The structure of [Fe2(μ-CO)(CO)4(μ-Ph2PCH2PPh2)2] has been established X-ray crystallographically. The two iron atoms, which are bridged by a carbonyl group as well as by the two ditertiary phosphine ligands, are separated by a distance of 2.742(4) A, corresponding to a formal iron-iron bond.

Further studies of the reactivity of cyclopentadienyl, substitutedcyclopentadienyl and indenyl ligands withM2Cl2(NMe2)4(M = Mo or W). Crystal and molecular structuresofMo2(C9H7)2(NMe2)4 andW2(C5H4Me)2(NMe2)4

Metathetic reactions employing 1,2-M 2 Cl 2 (NMe 2 ) 4 compounds (M = Mo or W) and the sodium or lithium salts of cyclopentadienyl (Cp), methylcyclopentadienyl, indenyl (C 9 H 7 ) and bis(methyl)bis(cyclopentadienyl)silyl, Me 2 Si(C 5 H 4 ) 2 2- , anions carried out in hydrocarbon or ether solvents have led to the isolation of orange, hydrocarbon-soluble, air-sensitive crystalline solids of formula 1,2-M 2 R 2 (NMe 2 ) 4 . In solution the NMR data are consistent with C 2 symmetry and restricted rotation about the M–N bonds. The complexes where R = C 5 H 5 show only one CH resonance in their 1 H NMR spectra consistent with ring whizzing. The solid-state and molecular structures of Mo 2 (C 9 H 7 ) 2 (NMe 2 ) 4 and W 2 (C 5 H 4 Me) 2 (NMe 2 ) 4 reveal that the indenyl and C 5 H 4 Me ligands are η 3 -bonded to the MM 6+ moiety with three M–C distances within the range 2.35 to 2.52 A and two distinctly larger, ca. 2.75–2.80 A. The M–M distances, 2.252(1) A (M = Mo) and 2.345(1) A (M = W) and M–N distances, 1.96 to 1.99 A, are similar to those for 1,2-M 2 R 2 (NMe 2 ) 4 compounds, where R = alkyl or aryl. The linked Cp complex W 2 [(C 5 H 4 ) 2 SiMe 2 ] (NMe 2 ) 4 was found to show similar structural features although the molecular structure suffered from disorder. The data reported, together with previous results, show that cyclopentadienyl ligands compete favorably with the NMe 2 ligand as σ 2 π 2 donors, η 3 -C 5 . The η 5 -C 5 mode is not favoured (on electronic grounds) because this would require disruption of the M–M triple bond in the presence of four Me 2 N σ 2 π 2 donors.