Dmpe Complex Research Articles

Complexes of trimethylsilyl trifluoromethanesulfonate with nitrogen, oxygen, and phosphorus donors

The Lewis acceptor chemistry of Me3SiOTf with p-block Lewis bases has been explored and a library of complexes has been characterized by spectroscopic and, where possible, crystallographic methods. Compounds with the generic formula [Me3Si(L)][OTf] (L = 4-dmap, pyr, imz, OPMe3, OPCy3, OPPh3, OpyrMe, dmso, PMe3) were isolated from 1:1 mixtures of Me3SiOTf and the respective ligand in CH2Cl2. Characterization by NMR spectroscopy confirmed the solution stability of all but [Me3Si(PMe3)][OTf], with indications that the latter dissociates into PMe3 and Me3SiOTf. Solid-state structures of [Me3Si(4-dmap)][OTf], [Me3Si(pyr)][OTf], [Me3Si(OPCy3)][OTf], [Me3Si(OPPh3)][OTf], [Me3Si(OpyrMe)][OTf], and [Me3Si(PMe3)][OTf] were elucidated by single crystal X-ray diffraction, confirming the envisaged ionic formulations resulting from the displacement of the OTf anion from the silicon center of Me3SiOTf by the incoming ligand. Mixtures of Me3SiOTf with other related donors, including ChPPh3 (Ch = S or Se), NEt3, SMe2, PPh3, 2,2′-bipy, or Me2CO, show no evidence of reaction under ambient conditions, reflecting the lower basicity and (or) greater steric encumbrance of these ligands. Reactions of Me3SiOTf with bis-donor ligands yielded complexes of the generic formulae [Me3Si(L–L)SiMe3][OTf]2 (L–L = 4,4′-bipy, tmeda, dmpe) and [Me3Si(L–L)][OTf] (L–L = 4,4′-bipy, tmeda, dmpe). The tmeda and dmpe complexes, however, were found to dissociate in solution, with complexes only prevailing in the solid phase. X-ray diffraction studies of [Me3Si(4,4′-bipy)SiMe3][OTf]2 and [Me3Si(dmpe)SiMe3][OTf]2 confirmed the expected connectivities and ionic formulations, with Si–ligand bond lengths comparable to those observed in [Me3Si(pyr)][OTf] and [Me3Si(PMe3)][OTf], respectively.

Synthetic and computational studies of the palladium(iv) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C–C reductive elimination

Synthetic routes to methyl(aryl)alkynylpalladium(IV) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from Pd(IV) centres. The iodonium reagents IPh(C≡CR)(OTf) (R = SiMe(3), Bu(t), OTf = O(3)SCF(3)) oxidise Pd(II)Me(p-Tol)(L(2)) (1-3) [L(2) = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d(6) or toluene-d(9) at -80 °C to form complexes Pd(IV)(OTf)Me(p-Tol)(C≡CR)(L(2)) [R = SiMe(3), L(2) = dmpe (4), bpy (5), phen (6); R = Bu(t), L(2) = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C≡CR above ~-50 °C. NMR spectra show that isomeric mixtures are present for the Pd(IV) complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between -80 °C and -60 °C observed for the dmpe complex 4 in toluene-d(8). Kinetic data for reductive elimination from Pd(IV)(OTf)Me(p-Tol)(C≡CSiMe(3))(dmpe) (4) yield similar activation parameters in acetone-d(6) (66 ± 2 kJ mol(-1), ΔH(‡) 64 ± 2 kJ mol(-1), ΔS(‡)-67 ± 2 J K(-1) mol(-1)) and toluene-d(8) (E(a) 68 ± 3 kJ mol(-1), ΔH(‡) 66 ± 3 kJ mol(-1), ΔS(‡)-74 ± 3 J K(-1) mol(-1)). The reaction rate in acetone-d(6) is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol(-1)), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible C-C coupling products (13.0 kJ mol(-1)). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC≡CSiMe(3) and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp(2) for p-Tol, sp for C≡C-SiMe(3)) to form the product with the strongest C-C bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me(3)SiC≡C trans to OTf. Crystal structure analyses are presented for Pd(II)Me(p-Tol)(dmpe) (1), Pd(II)Me(p-Tol)(bpy) (2), and the acetonyl complex Pd(II)Me(CH(2)COMe)(bpy) (11).

Synthesis and characterization of phosphine adducts of thorium borohydride, Th(BH 4) 4: Crystal structures of Th(BH 4) 4(PEt 3) 2 and Th(BH 4) 4(Me 2PCH 2CH 2PMe 2) 2

Addition of tertiary phosphines to Th(BH 4) 4(Et 2O) 2 yields the new Lewis base adducts, Th(BH 4) 4(PMe 3) 2, Th(BH 4) 4(PEt 3) 2, and Th(BH 4) 4(dmpe) 2, where dmpe = 1,2-bis(dimethylphosphino)ethane. If one considers the BH 4 − groups to occupy one coordination site, then Th(BH 4) 4(PEt 3) 2 adopts a trans-octahedral geometry, and Th(BH 4) 4(dmpe) 2 adopts a trigonal dodecahedral geometry with the dmpe ligands bridging between the “inner” sites. In the PMe 3 and PEt 3 complexes, all four BH 4 − groups are κ 3, whereas in the dmpe complex two of the BH 4 − groups are κ 2 and two are κ 3. In the dmpe complex, the Th⋯B distances to the κ 2 and κ 3 BH 4 − groups are 2.91 and 2.69 Å, respectively. All of the Lewis base adducts of Th(BH 4) 4 are volatile and may be sublimed in vacuum. They have been characterized by infrared and 1H, 11B, and 31P NMR spectroscopy. The results show that thorium complexes of unidentate phosphines can be made and are stable enough to isolate and characterize. 31P NMR coordination chemical shifts of thorium phosphine complexes are on the order of 30–45 ppm. The compound Th(BH 4) 4(dmpe) 2 is the first thorium complex to contain κ 2 BH 4 − groups.

Preparation, crystal structures and spectroscopic properties of novel [M IIICl 3 − n(P) 3 + n] n+ (M = Co, Rh; n = 0, 1, 2 or 3) series of complexes containing tripodal tridentate phosphine, 1,1,1-tris(dimethylphosphinomethyl)ethane

Cobalt(III) and rhodium(III) complexes of the series of [M IIICl 3 − n (P) 3 + n ] n+ (M = Co or Rh; n = 0, 1, 2 or 3) have been prepared with the use of 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) and mono- or didentate phosphines. The single-crystal X-ray analyses of both series of complexes revealed that the M–P and M–Cl bond lengths were dependent primarily on the strong trans influence of the phosphines, and secondarily on the steric congestion around the metal center resulting from the coordination of several phosphine groups. In fact, the M–P(tdmme) bonds became longer in the order of [MCl 3(tdmme)] < [MCl 2(tdmme)(PMe 3)] + < [MCl(tdmme)(dmpe)] 2+ (dmpe = 1,2-bis(dimethylphosphino)ethane) < [M(tdmme) 2] 3+ for both Co III and Rh III series of complexes, while the M–Cl bond lengths were shortened in this order (except for [M(tdmme) 2] 3+). Such a steric congestion around the metal center can also account for the structural and spectroscopic characteristics of the series of complexes, [MCl(tdmme)(dmpm, dmpe or dmpp)] 2+ (dmpm = bis(dimethylphosphino)methane, dmpp = 1,3-bis(dimethylphosphino)propane). The X-ray analysis for [CoCl(tdmme)(dmpm or dmpe)](BF 4) 2 showed that all Co–P bonds in the dmpm complex were shorter by 0.03–0.04 Å than those in the dmpe complex. Furthermore, the first d–d transition energy of the Co III complexes and the 1 J Rh–P(tdmme) coupling constants observed for the Rh III complexes indicated an unusual order in the coordination bond strengths of the didentate diphosphines, i.e., dmpm > dmpe > dmpp.

Syntheses, Structures and Spectroscopic Properties of Mixed-Ligand Chromium(III) Complexes Containing 1,2-Bis(dimethylphosphino)ethane, 1,3-Bis(dimethylphosphino)propane or 1,1,1-Tris(dimethylphosphinomethyl)ethane

Abstract Mixed-ligand chromium(III) complexes containing di- or tridentate phosphines, trans-[CrX2(dmpe)2]+ (X = Cl, Br, I, CN, NCS or N3; dmpe = Me2P(CH2)2PMe2), trans-[CrX′2(dmpp)2]+ (X′ = Cl, Br or I; dmpp = Me2P(CH2)3PMe2), [CrX′′3(tdmme)] (X′′ = Cl, Br, CN or NCS; tdmme = MeC(CH2PMe2)3) and [CrCl2(tdmme)(PMe3)]+, have been prepared and their structures and spectroscopic properties have been investigated. The single-crystal X-ray analyses of trans-[CrI2(dmpp)2]I (6) and [Cr(CN)3(tdmme)]·2H2O (16·2H2O) have also been reported. The Cr–P bond length in 6 (2.5147(6) Å) is longer than those in trans-[CrCl2(dmpe)2]BPh4 (av 2.445 Å) and in 16·2H2O (av 2.455 Å). In the UV-vis absorption spectra of trans-[Cr(Cl or Br)2(dmpe or dmpp)2]+, an intense (ε &amp;gt; 1000 dm3 mol−1 cm−1) absorption envelope is observed at 20000–30000 cm−1, in addition to the 4B1 → a4E d–d transition band at ∼17000 cm−1 (ε = 44–65 dm3 mol−1 cm−1). The envelope consists of three d–d transition components: 4B1 → 4A2, 4B2 and b4E, similar to the corresponding H2N(CH2)2NH2 (= en) complexes. The magnetic circular dichroism (MCD) spectra of these didentate phosphine complexes show a spin-forbidden d–d transition (4B1 → 2E, 2B2) component at ∼19000 cm−1. The ligand-field and Racah parameters, Δ(d), Δ(e), Δ(t2) and B, of the complexes are estimated. It is found that the ligand-field and repulsion parameters of the dmpp complexes are almost the same as those of the corresponding en complexes. For the dmpe complexes, while Δ(d) is just slightly smaller than those of the dmpp and en complexes, the tetragonal symmetry parameters, Δ(e) and Δ(t2), are much reduced. The ligand-field perturbation energies of phosphines are estimated as Δdmpp = 21830 &amp;gt; Δtdmme = 20920 &amp;gt; Δdmpe = 20620 cm−1, the order of which is strange, since the Cr–P bond lengths in the complexes increase in the order of dmpp &amp;gt; tdmme &amp;gt; dmpe. Furthermore, the interelectronic repulsion parameter B of [Cr(Cl or Br)3(tdmme)] estimated from the 4A2 → 4T1 transition energy (B35) is remarkably much smaller than the parameter estimated from the spin-forbidden 4A2 → 2T2 transition energy (B55).

Synthesis and characterization of phosphine adducts of the open zirconocene Zr(C 5H 7) 2

Reactions of either P(CH 3) 2C 6H 5 or dmpe (dmpe = (CH 3) 2PC 2H 4P(CH 3) 2) adducts of ZrCl 4 with four equivalents of KC 5H 7 lead to the formation of the respective 16 or 18 electron mono(ligand) adducts of the open zirconocene Zr(C 5H 7) 2. Both complexes were found to exist in the expected symmetric conformations, as confirmed for the dmpe complex by a single crystal X-ray diffraction study.

Density functional calculations on agostic ethyl-Ti (IV) complexes

First principles, density functional theory embodied in the DMol program has been applied to agostic ethyl-Ti-complexes, including the dmpe complex, [Ti(-CH 2CH 3)C1 3(dmpe)], where dmpe=(Me 2PCH 2) 2 and its model complex, [Ti(−CH 2CH 3)Cl 3(PH 3) 2]. The ethyl moiety of the complexes can adopt two limiting conformations, staggered and eclipsed. In the model complex, [Ti(−CH 2CH 3)C1 3(PH 3) 2], both conformers are found to form agostic structures upon geometry optimization subject to Cs symmetry constraint, with the agostic eclipsed structure being the lower in energy. Full geometry optimization of the dmpe complex, [Ti(−CH 2CH 3)C1 3(dmpe)], yields an agostic structure with geometrical features similar to those measured by single crystal X-ray analysis. It is shown that the HOMO orbital contributes substantially to the agostic bonding.

Synthesis, crystal structures and spectroscopic properties of cis- and trans-[RhCl2L2]+[L = 1,3-bis(dimethylphosphino)propane or 1,2-bis(dimethylphosphino)ethane (dmpe)]: reinvestigation of the dmpe complexes

Download options Please wait... Article information DOI https://doi.org/10.1039/DT9950003609 Article type Paper Download Citation J. Chem. Soc., Dalton Trans., 1995, 3609-3616 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Synthesis, crystal structures and spectroscopic properties of cis- and trans-[RhCl2L2]+[L = 1,3-bis(dimethylphosphino)propane or 1,2-bis(dimethylphosphino)ethane (dmpe)]: reinvestigation of the dmpe complexes T. Suzuki, K. Isobe and K. Kashiwabara, J. Chem. Soc., Dalton Trans., 1995, 3609 DOI: 10.1039/DT9950003609 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Takayoshi Suzuki Kiyoshi Isobe Kazuo Kashiwabara

Unsaturated Bis(phosphido)‐bridged Heterobimetallic Polyhydrides via Dihydrogen Activation

AbstractHydrogenation (1 atm) of (PCy2)2Re(μ‐PCy2)2M(1,5‐COD) (M = Rh, Ir; Cy = cyclohexyl; COD = cyclooctadiene), (PCy2)2Re(μ‐PCy2)2Rh(DMPE) (DMPE = [Me2PCH2]2), [(PCy2)2ReH(μ‐PCy2)2Rh(DMPE)]BF4 and (PCy2)2ReH(μ‐PCy2)2Pd‐(PPh3) proceeds stepwise with initial additions of H2 across the Re = P multiple bonds to give ReH(PCy2H) moieties. Further addition of H2 occurs only for M = Rh. The DMPE complex gives the tetrahydride (PCy2H)2ReH3(μ‐PCy2)2RhH(DMPE), which loses PCy2H at 80 °C to give (PCy2H)ReH4(μ‐PCy2)2Rh(DMPE). Hydrogenation of the COD complex affords the stable hexahydride (PCy2H)ReH5(μ‐PCy2)2RhH(PCy2H) via the cyclooctenyl complex. (PCy2)2ReH(μ‐PCy2)2Rh(η3‐C8H13). While the hexahydride is an active homogeneous catalyst precursor for the hydrogenation of alkenes, dienes, and alkynes, attempts to activate the Re center for C‐H bond activation have not yet been successful. 31P and 1H DNMR spectroscopy have been used to investigate the solution dynamics of the heterobimetallic polyhydrides, and several X‐ray diffraction studies serve to define the solid state structures.

Synthesis, Characterization and Evaluation of 99Tc/ 99mTc DIARS and DMPE complexes containing pentadecanoic acid

The synthesis and purification of two new ligands, 15-[bis(3,4-dimethyl arsino)phenyl]pentadecanoic acid (FA-DIARS) and [bis(16,17-dimethyl phosphino)]heptadecanoic acid (FA-DMPE) and the preparation of their corresponding 99Tc/ 99mTc complexes of the general formula [Tc (III) L 2Cl 2] +, wherein L is FA-DIARS or FA-DMPE are reported. After careful purification by preparative HPLC, the 99Tc complexes were characterized by spectroscopy, while the 99mTc complexes were used to determine the biodistribution in mice. The results of the organ distribution studies indicated a relatively high uptake in heart (5–7% dose/g). The complexes were, however, found to be very slowly cleared from the blood, probably due to strong binding to serum proteins. Further, the heart to liver and heart to lung ratios were unfavourable. Attempts to improve the efficacy by synthesizing complexes containing one fatty acid per molecule are also described.

Paramagnetic carbenemetal complexes. Part 1. Cationic chromium(I) complexes and the chemistry of their chromium(0) precursors and of related molybdenum(0) and Tungsten(0) complexes, especially with bulky carbene ligands C(OR′)R[R  CH(SiMe3)2or CH2SiMe3

Carbenemetal complexes having bulky alkyl substituents at Ccarb., [M(CO)5{C(OR′)R}][M = Cr, Mo, or W; R = CH2CMe3, CH2SiMe3, or CH(SiMe3)2; R′= Me, Et, or SiMe3], are reported; a noteworthy feature is the good thermal stability of the molybdenum(0) complexes. Photolysis of [Cr(CO)5L][L = C(OEt)CH(SiMe3)2 or [graphic omitted]Et (abbreviated as LEt)] in the presence of P(OPh)3, dmpe, or dppe yields fac-[Cr(CO)3(L)L′2][L′= P(OPh)3 or L′2= Me2P(CH2)2PMe2(dmpe) or Ph2P(CH2)2PPh2(dppe)]. Addition of Ag[BF4] to the latter in CH2Cl2 affords [Cr(Co)3(L)L′2]+, characterised by e.s.r. spectroscopy. The dmpe complex with L = LEt is stable at ambient temperature [unlike the other two chromium(I) analogues] and is well characterised, m.p. 95 °C, as is [Cr(CO)3{C(OEt)CH(SiMe3)2}(dmpe)][BF4]. The gav factors for the 10 new chromium(I) salts are ca. 2.02 which suggests that significant unpaired spin is delocalised away from the metal, consistent with the low 53Cr isotropic, hyperfine coupling constant (ca. 1.3 mT). Detailed i.r., 1H and 13C n.m.r., and He(l) photoelectron spectroscopic, as well as mass spectrometric, data are described for the carbenemetal(0) complexes.