- Catalytic P-H activation by Ti and Zr catalysts
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Catalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts [Cp*2Zr(μ-H) 3Li]3 (1a) or [Cp*2Zr(μ H) 3K(thf)4] (1b), and the metallocycles [CpTi(NPtBu 3)(CH2)4] (6) and [Cp*M(NPtBu 3)(CH2)4] (M = Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH2 (R = Ph, C6H2Me3, Cy, C10H7) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP)n (n = 4, 5) while reaction of tBu3C6H2PH 2 gave the phosphaindoline fBu2(Me2C-CH 2)C6H2PH (9). Stoichiometric reactions of these catalyst precursors withprimary phosphines afforded [Cp* 2Zr((PR)2)H][K(thf)4] (R = Ph 2, Cy 3, C 6H2Me3 4), [Cp*2Zr((PPh) 3)H] [K(thf)4] (5), [CpTi(NPtBu3)(PPh) 3] (7) and [CpTi(NPfBu3)(nrPHPh)]2 (8), while reaction of 6 with (C6H2tBu3)PH2 in the presence of PMe3 afforded [CpTi(NPtBu3)(PMe 3)(P(C6H2tBu3)] (10). The secondary phosphines Ph2PH and (PhHPCH2)2CH2 also undergo dehydrocoupling affording (Ph2P)2 and (PhPCH2)2CH2. The bisphosphines (CH 2PH2)2 and C6H4(PH 2)2 are dehydrocoupled to give (PCH2CH 2PH)v (12) and (C6H4P(PH)) 2 (13) while prolonged reaction of 13 gave (C6H 4P2)8 (14). The analogous bisphosphine Me 2C6H4(PH)2 (17) was prepared and dehydrocoupling catalysis afforded (Me2C6H 2P(PH))2 (18) and subsequently [(Me2C 6H2P2)2(μ-Me2C 6H2P2)]2 (19). Stoichiometric reactions with these bi-sphosphines gave [Cp*2Zr(H)(PH)2C 6H4][Li(thf)4] (22), [CpTi(NPtBu 3)(PH)2C6H4]2 (23) and [Cp*Ti(NPfBu3)(PH)2C6H4] (24). Mechanistic implications are discussed.
- Masuda, Jason D.,Hoskin, Aaron J.,Graham, Todd W.,Beddie, Chad,Fermin, Maria C.,Etkin, Nola,Stephan, Douglas W.
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p. 8696 - 8707
(2007/10/03)
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- Synthesis of 1,2-bis[(diorgano)phosphino]ethanes via Michaelis-Arbuzov type rearrangements
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A three-step process for the synthesis of the bis(diorganophosphino)ethanes R2PCH2CH2PR2 where R = Et, Ph, iPr, Cy and tBu was examined. In the first step, diorganochlorophosphines were allowed to react with ethylene glycol in the presence of triethylamine at room temperature in THF solution. For R = Ph, iPr and Cy, the bisphosphinites R2POCH2CH2OPR2 were obtained in high yield. For R = Et, the bisphosphinite could not be isolated but may be formed in 80% mixtures with tetraethyldiphosphine, Et2PPEt2, as a minor component. The reaction of di-t-butylchlorophosphine with ethylene glycol occurs at temperatures greater than 130 °C giving di-t-butyl phosphine oxide, tBu2PH(O), as the only phosphorus-containing product. Thermolysis of the bisphosphinites R2POCH2CH2OPR2 (R = Ph, iPr and Cy) at 190-260 °C for 24 h gave the bisphosphine oxides, R2P(O)CH2CH2(O)PR2 in 9% (Ph), 90% (iPr) and 93% (Cy) yields. A DSC study of the thermal rearrangement of Cy2POCH2CH2OPCy2 to Cy2P(O)CH2CH2(O)PCy2 yielded an enthalpy of isomerization of -40.4 ± 0.6 kcal mol-1. Reduction of the bisphosphine oxides, R2P(O)CH2CH2(O)PR2 (R = Ph, iPr and Cy) with trichlorosilane gave the bisphosphines, R2PCH2CH2PR2 in 80-85% yield. The overall yields of the bisphosphines R2PCH2CH2PR2 (R = iPr and Cy) in the three-step process were 61 and 75%, respectively, suggesting that this process should be an attractive synthetic pathway to these two bisphosphines.
- Baldwin, Lawrence C,Fink, Mark J
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p. 230 - 238
(2007/10/03)
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- Dehydrocoupling of phosphanes catalyzed by a rhodium(I) complex
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Two reaction protocols have been developed for the catalytic dehydrocoupling of secondary phosphanes by the rhodium(I) complex [Cp*Rh{CH2=CH(TMS)}2]: In the presence of an olefin, transfer hydrogenation occurs to give the corresponding alkane and the diphosphane. Without the addition of an olefin, the reaction proceeds by loss of dihydrogen but more elevated reaction temperatures must be used [Eq. (1)].
- Boehm, Volker P. W.,Brookhart, Maurice
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p. 4694 - 4696
(2007/10/03)
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- Lewis acidic titanium species: the synthesis, structure, bonding and molecular modelling considerations of the complexes Ti(NR2)3Cl (R = Me, Et)
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Reaction of simple amides with TiCl4 affords mixed amido-chloride species Ti(NR2)4-nCln.The trisamide-chloride species Ti(NR2)3Cl can be prepared directly employing three equivalents of amide or by reaction Ti(NR2)4 with TiCl4.The compound Ti(NMe2)3Cl, 1, crystallizes in the trigonal space group , with a = 11.525(5), c = 14.939(3) Angstroem, Z = 6, and V = 1718(1) Angstroem3.The compound Ti(NEt2)3Cl, 2, crystallizes in the monoclinic space group P21/c, with a = 8.385(2) Angstroem, b = 15.958(2) Angstroem, c = 14.230(4) Angstroem, β = 107.79(1) deg, Z = 4, and V = 1813(1) Angstroem3.The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral.The structural data are consistent with Ti-N multiple bonding.Preliminary results of EHMO calculations are consistent with d?-p? Ti-N bonding.Attempts to replace the halides with phosphides (LiPR2, R = Me, Et, Ph) led not to the Ti(IV) phosphido species, but rather to redox chemistry yielding Ti(III) amides and P2R4.The barrier to rotation about the Ti-N bonds has been considered.Variable temperature 1H NMR studies reveal that the barrier is small.Extended Hueckel total energy minimization calculations have been performed.In addition, MMX calculations of the barrier Ti-N rotation are reported.The results of these calculations imply that the rotational barrier is dominated by steric effects. Key words: titanium amides, structures, Ti-N bonding.
- Dick, David G.,Rousseau, Roger,Stephan, Douglas W.
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p. 357 - 362
(2007/10/02)
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- Electron-transfer chemistry of (Me5C5)2Yb: Cleavage of diorganoperoxide and related chalcogenides to give (Me5C5)2Yb(ER)(L) (E = O, S, Se, or Te; L = a Lewis base). Crystal structure of (Me5C5)2Yb(TePh)(NH3)
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The divalent metallocenes of ytterbium (Me5C5)2Yb(OEt2) or (Me5C5)2Yb(NH3)2 react with molecules of the type REER to give the trivalent ytterbium complexes (Me5C5)2Yb(ER)(L), where L is OEt2 or NH3, E is S, Se, or Te, and R is a phenyl or substituted phenyl group. The ammonia complexes are easier to characterize than the diethyl ether complexes since the latter complexes lose ether in the solid state and give unsatisfactory microanalytical data whereas the ammonia complexes give satisfactory elemental analyses. In addition, the line width of the Me5C5 protons in the 1H NMR spectra of the diethyl ether complexes is ca. 500 Hz whereas the line width at half-height is ca. 50 Hz for the ammonia complexes, consistent with the notion that the barrier to chemical exchange is higher for the ammonia complexes. The peroxides ROOR, where R is Me3C or Me3Si, give the alkoxides (Me5C5)2Yb(OR)(NH3), and Et2NC(S)SS(S)CNEt2 gives the known (Me5C5)2Yb(S2CNEt2). In contrast, dialkyl dithiophosphinates give (Me5C5)2Yb(S2PR2) and R2PPR2, where R is Me or Et. The synthetic routes developed in this work are the best methods currently available for synthesis of these trivalent species. The crystal structure of (Me5C5)2Yb(TePh)(NH3) has been done. The crystals are orthorhombic, P212121, with a = 11.823 (3) ?, b = 25.917 (6) ?, c = 8.539 (2) ?, and V = 2616.5 ?3. For Z = 4, the calculated density is 1.69 g cm-3. The structure was refined by full-matrix least squares to a conventional R factor of 0.046 [4991 data, F2 > σ(F2)]. The Yb-Te distance is 3.039 (1) ?, and the Yb-Te-C(Ph) angle is 113.0 (3)°.
- Berg, David J.,Andersen, Richard A.,Zalkin, Allan
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p. 1858 - 1863
(2008/10/08)
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