摘要:

The first example of simple orthometallation of a bis(diphenylphosphino)methane ligand at a binuclear centre is reported. Both dppm ligands of the binuclear ruthenium(0) complex [Ru2(CO)5(µ-dppm)2],1, are orthometallated when the complex is heated in benzene solution to yield the unusual complex [Ru2(CO)4-(Ph2PCH2PPhC6H4)2],2. The structure of2was determined crystallographically (monoclinic,P21/n,a = 21.349(4),b = 12.209(5),c = 22.457(5) Å, β = 104.34(2)°,Z = 4,R,Rw = 0.0658, 0.0561) and the unusual cyclometallated complex was also characterized spectroscopically. The cyclometallation occurs in such a way that each ligand gives rise to two fused five-membered rings, RuRuPCP and RuRuPCC, fused at the Ru—Ru and Ru—P bonds.Keywords: ruthenium, bis(diphenylphosphino)methane, metallation.

ISSN:0008-4042    

DOI:10.1139/v95-113

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Treatment of [Ni2(µ-Br)2(η3-C3H5)2] with Na2[nido-7,9-C2B10H12] in THF (tetrahydrofuran) affords the anionic species [Ni(η3-C3H5)(η6-7,9-C2B10H12)]−, which was isolated as its [NEt4]+salt8a. A similar reaction between Na2[nido-7,9-Me2-7,9-C2B10H10] and [Ni2(μ-Br)2(η3-C3H5)2] in thf gives the anionic species [Ni(η3-C3H5)(η6-7,9-Me2-7,9-C2B10H10)]−isolated as [N(PPh3)2]+(8b) and [NEt4]+(8c) salts, respectively. The molecular structure of8bhas been established by X-ray diffraction. Crystals are monoclinic, space groupP21/c(No. 14) witha = 14.685(3) Å,b = 18.346(2) Å,c = 16.319(1) Å, β = 99.93(1)°, andZ = 4. The nickel atom is ligated by thenido-7,9-Me2-7,9-C2B10H10cage in an η6manner, as well as by the allyl group, with the latter adopting an η3-bonding mode (Ni—C = 2.023(5), 1.939(8), and 1.988(5) Å). The palladium analog8dwas similarly prepared from Na2[nido-7,9-Me2-7,9-C2B10H10] and [Pd2(µ-Cl)2(η3-C3H5)2], followed by addition of [NEt4]Cl•H2O, but in contrast with the nickel species this product was unstable, especially its solutions in air.Keywords: nickel, palladium, allyl complex, carborane.

ISSN:0008-4042    

DOI:10.1139/v95-114

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

TheO,O-alkylene dithiophosphate derivatives of triphenyl- and diphenylgermane,andhave been prepared and characterized by infrared, Raman, and1H,13C, and31P NMR spectroscopy, mass spectrometry, and, in three cases, X-ray crystallography.1, crystallizes as monoclinic in the space groupP21/a(No. 14) with the cell parametersa = 12.868(5) Å,b = 11.354(4) Å,c = 17.207(4) Å, β = 95.42(2)°,V = 2502(1) Å3,Z = 4,R = 0.0640, andRw = 0.0585.2, crystallizes as orthorhombic in the space groupPbca(No. 61) with the cell parametersa = 23.007(4) Å,b = 16.840(4) Å,c = 12.068(3) Å,V = 4657(3) Å3,Z = 8,R = 0.0502, andRw = 0.0329.3, crystallizes as monoclinic in the space groupC2/c(No. 15) with the cell parametersa = 35.48(2) Å,b = 9.275(5) Å,c = 20.78(1) Å, β = 120.93(3)°V = 5866(5) Å3,Z = 8,R = 0.0674, andRw = 0.0562. As with their methylgermanium analogues, the environment about germanium is essentially that of a distorted tetrahedron, with the terminal sulfur atoms oriented towards germanium rather than away from it, in contrast with analogous noncyclic dithiophosphatogermanes. The substituents on the atoms in both the five- and six-membered rings maintain their nonequivalence in solution, in contrast with tin analogues.Keywords: structure, germanium, diphenyl, triphenyl, cyclic dithiophosphates

ISSN:0008-4042    

DOI:10.1139/v95-115

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The reaction of Ru(CO)4(C2H4) or Ru(CO)5with 1,5-Ph4P2N4S2in CH2Cl2-hexane at 23 °C produces the dimer [Ru(CO)2(Ph4P2N4S2)]2(4) in 54% and 11% yields, respectively. The treatment of4with methyl triflate (1:1 molar ratio) in dichloromethane yields the mono(N-methylated) derivative [Ru2(CO)4(Ph4P2N4S2)(Ph4P2N4S2Me)][CF3SO3] (5) or, in a 1:2 molar ratio, the dimethylated derivative [Ru(CO)2(Ph4P2N4S2Me)]2[CF3SO3]2, which exists as a ca. equal mixture of two symmetrical isomers on the basis of1H and31P NMR, and IR spectra. The reaction of4with two equivalents of Me3NO in the presence of acetonitrile generates [Ru(CO)(CH3CN)(Ph4P2N4S2)]2, which is also formed as a mixture of isomers in a ratio of ca. 2:1 on the basis of1H and31P NMR, and IR spectra. The X-ray structure of4•CH2Cl2shows that the P2N4S2ring is bonded to one ruthenium through two (geminal) nitrogen atoms and the remote sulfur atom while the second sulfur atom acts as a bridge to the other ruthenium. The crystals of4•CH2Cl2are triclinic, space groupwitha = 12.901(1) Å,b = 13.072(1) Å,c = 10.123(1) Å, α = 100.88(1)°, β = 98.90(1)°,γ = 67.50(1)°,V = 1542.4(3) Å3, andZ = 2. The finalRandRw, values were 0.040 and 0.027, respectively. The X-ray structure of5reveals that N-methylation does not significantly perturb the bonding between the heterocyclic ligand and ruthenium. The crystals of5are triclinic, space groupwitha = 12.912(6) Å,b = 13.435(7) Å,c = 9.948(3) Å, α = 105.04(3)°, β = 102.85(3)°, γ = 70.74(4)°,V = 1555(1) Å3, andZ = 2. The finalRandRwvalues were 0.063 and 0.071, respectively.Keywords: ruthenium, tetradentate ligand, P2N4S2ring.

ISSN:0008-4042    

DOI:10.1139/v95-116

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

[Cp*Ir(C2H4)(N2Ar)][BF4] (1BF4; Ar = p-N2C6H4OMe) has been synthesized by reacting [ArN2] [BF4] with Cp*Ir(C2H4)2at low temperature. An initial electrophilic attack of the incoming diazonium ion at iridium, followed by expulsion of C2H4, is postulated to account for the mild reaction conditions that are in sharp contrast to the usual inertness of the bis(ethylene) compound toward ligand substitution. The IR and nitrogen NMR data for1BF4and its15Nαderivative unambiguously establish that the ArN2ligand has the singly bent geometry in this complex in solution. The X-ray crystal structure confirms this for the solid state, and establishes that the plane of the aryldiazenido ligand is approximately perpendicular to the plane defined by the Ir atom and the centers of mass of the Cp* and ethylene ligands. An extended Hückel molecular orbital analysis of the singly bent aryldiazenido ligand has been carried out and satisfactorily accounts for the observed orientation of the ArN2ligand. An analysis of the variable-temperature1H and13C NMR of1BF4indicates thatbothrestricted rotation of the C2H4ligand and a conformational isomerization of the aryldiazenido ligand are occurring, and ΔG≠270for the ethylene rotation barrier is estimated at ≤ 51.5 ± 0.4 kJ mol−1. This is lower than the barrier of ΔG≠353 = 68.7 ± 0.2 kJ mol−1determined previously for the analogous nitrosyl complex [Cp*Ir(C2H4)(NO)] [BF4] (2BF4) and it is suggested that in these half-sandwich complexes both NO and ArN2function as single-faced π-acceptors, and in these circumstances ArN2is the better π-acceptor. The ethylene in1BF4is readily displaced by PPh3to give [Cp*Ir(PPh3)(N2Ar)][BF4] (3BF4). This reacts with NaBH4to yield Cp*IrH(PPh3)(N2Ar) (4) in which the ArN2ligand has switched to the doubly bent geometry, on the basis of the15NαNMR chemical shift data. Attempts to synthesize the corresponding chloro analogue5resulted in only the chloride salt of the singly bent ArN2cation3. For example, reaction of3BF4with HCl yields the aryldiazene complex [Cp*IrCl(PPh3)(NHNAr)] [BF4] (6), but deprotonation of this with Et3N yields3Cl, not5. Compound1BF4crystallized in the space groupP21/nwitha = 8.5780(10) Å,b = 20.5310(23) Å,c = 12.0310(15) Å, β = 93.500(10)°, andZ = 4. The structure was refined to Rf = 0.0281 on the basis of 2611 observed reflections withI°> 2.5σ(Io) in the range 2θ = 0–50° (Mo-Kα).Keywords: iridium, cyclopentadienyl, aryldiazenido, nitrosyl, ethylene.

ISSN:0008-4042    

DOI:10.1139/v95-117

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The compounds [Cl2CpTi]2(OCH2CH2CH2O)1, [Cl2CpTi]2(OCH2CMe2CH2O)2, and [Cl2CpTi]2-(OCHMeCH2CHMeO)3were prepared from the reactions of CpTiCl3and the bis-trimethylsilyl ethers of the diols. Alternatively, these species could be made from the reactions of the diol, imidazole, and CpTiCl3employing the appropriate stoichiometry. In the presence of excess diol, loss of CpH is observed. In the case of 1,3-propanediol the species [TiCl(HOCH2CH2CH2O)(OCH2CH2CH2O)]24was isolated. Recrystallization of4from THF led to the isolation of [TiCl2(OCH2CH2CH2O)(THF)]25, albeit in very low yield. This chemistry is described and the implications are considered. Compounds1,3,4, and5were characterized crystallographically; the parameters are summarized as follows:1:C2/c(No. 15),a = 12.587(2) Å,b = 9.632(2) Å,c = 15.824(3) Å, β = 107.88(1)°,V = 1811.3(5) Å3,Z = 4;3:C2/c(No. 15),a = 12.855(2) Å,b = 10.772(2) Å,c = 15.665(2) Å, β = 109.26(1)°,V = 2047.7(5) Å3,Z = 4;4:P21/n(No. 14),a = 8.911(3) Å,b = 7.821(2) Å,c = 13.986(2) Å, β = 102.56(2)°,V = 951.3(3) Å3,Z = 2;5:P21/n(No. 14),a = 8.693(3) Å,b = 9.286(2) Å,c = 13.411(2) Å, β = 101.18(2)°,V = 1062.1(4) Å3,Z = 2.Keywords: titanium alkoxides, structure, synthesis.

ISSN:0008-4042    

DOI:10.1139/v95-118

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Solid state ternary and quaternary metal nitrides containing a transition metal and one or two very electropositive metals such as alkali and (or) alkaline earth metals exhibit a number of structures containing low-coordinate transition metals in the transition metal – nitrogen subnetwork. Transition metal – nitrogen double and even triple bonds are found in these structures involvingdπ → pπ bonding from a filled transition metaldorbital to an otherwise empty nitrogenporbital. Such multiply bonded nitrogen atoms function as strong field ligands in contrast to amido ligands such as (Me3Si)2N−, which generally function as weak field ligands in transition metal chemistry. The transition metal environment in these ternary nitrides can be modelled by "banana bonds" from the polyhedron using the atomic orbitals required for both the σ- and π-bonding to the nitride ligands, e.g., the trigonal prism for the trigonal planar derivatives MIIIN36−(M = V, Cr, Mn, Fe) with three M=N double bonds as well as FeIIN24−in Li4FeIIN2with two Fe≡N triple bonds and the planar square for the discrete linear CoIN25−in LiSr2CoN2. Reasonable electron counts are also obtained for the anionic metal–nitrogen networks in Ca2FeN2, Sr2LiFe2N3, Ba2LiFe2N3, Li3FeN2, CaNiN, Li3Sr3Ni4N4, BaNiN, and Ba8Ni6N7.Keywords: chemical bonding, topology, nitrides, transition metals.

ISSN:0008-4042    

DOI:10.1139/v95-119

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A detailed NMR study of the peptide NAc-FDEKA-NH2in aqueous and in CD3OH/H2O solutions as well as theN-acetylpentapeptide amides YDEKA, VDEKA, GDEKA, and the protected tetrapeptide NAc-DEKA-NH2in methanolic solutions indicates the importance of the first amino acid (ati −1) on stabilizing the type I β-turn. The data illustrate the hydrophobic stabilization of this turn, which is present in FDEKA, YDEKA, and VDEKA. For GDEKA and DEKA, the NMR data indicate that this turn is not present. Molecular mechanics calculations support this conclusion and indicate that for FDEKA and GDEKA the type I β-turn is distorted in both the vacuum and the solvated structures. For the solvated structures, the Cα(i) − Cα(i + 3) distance is 4.87 Å for FDEKA and 6.00 Å for GDEKA, which are to be compared with the value of 4.64 Å for an ideal type I β-turn, i.e., the distortion is far greater in GDEKA than in FDEKA. The calculations can be interpreted to indicate the presence of two major conformations in solution.Keywords: β-turns, FDEKA, pentapeptide.

ISSN:0008-4042    

DOI:10.1139/v95-120

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The synthesis of a series of permethylindenyl (Ind*) rhodium(III) complexes, [(η5-C9Me7)RhCl(μ-Cl)]2, [(η5-C9Me7)RhLCl2] (L = PMe3, PMe2Ph, PPh3), and [(η5-C9Me7)Rh(PMe3)2Cl]+Cl−, is reported. The structure of [(η5-C9Me7)RhCl(μ-Cl)]2, (4) was determined, confirming the dimeric nature of the compound. Ruby red crystals of4are monoclinic, space groupC2/c, with four molecules per unit cell of dimensionsa = 18.598(5),b = 10.520(3),c = 17.376(3) Å and β = 115.10(2)°. The indenyl rings exhibit minimal distortion from perfect η5coordination to the Rh centres. A single crystal X-ray structure determination of [(η5-C9Me7)Rh(PMe2Ph)Cl2] (6) indicates a more distorted η5-coordination of the indenyl ligand, with the auxiliary ligand having the greatesttransinfluence, namely, the PMe2Ph group, beingtransto the indenyl ring junction C—C bond. Yellow prismatic crystals of6are orthorhombic, space groupP212121, with four molecules per unit cell of dimensionsa = 8.819(1),b = 15.303(3),c = 17.296(3) Å.Keywords: rhodium, indenyl, permethylindenyl, heptamethylindenyl, phosphine complex. X-ray structure.

ISSN:0008-4042    

DOI:10.1139/v95-121

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Calculations based on density functional theory have been carried out on the reaction between Cl2Ti+–ethyl (1) and ethylene. In this study1was taken as a model for the cationic metallocenes of group-4 elements, which have been developed by Kaminsky and Brintzinger as efficient catalysts for the polymerization of olefins. The ground state structure of1has a β-agostic conformation in which a single Cβ—H bond is directed towards the metal center. It was assumed that this conformation also serves as a model for the resting state of the growing chain attached to the cationic group-4 metallocenes between insertions. Two paths were considered for the reaction between1and ethylene. The first (2) has ethylene approaching the agostic Cβ—H bond, whereas ethylene in the second approach (3) attacks the Ti—Cαlink from the side opposite to the Cβ—H bond. The front-side attack (2) results in a transfer of hydrogen from the β-carbon of ethyl to ethylene and represents a chain-terminating step with an activation energy of 5.3 kcal/mol. It was not possible to locate a path leading to olefin insertion from the front-side attack (2). The back-side attack (3) resulted readily in insertion with an activation energy of 3.9 kcal/mol. The study made use of full transition state optimization as well as a tracing of the reaction paths by the intrinsic reaction coordinate (IRC) method of Fukui. Previous investigations have all assumed that olefin insertion takes place via a front-side approach (2) based on the known stereochemistry of α-olefin polymerization. The present study suggests that insertion takes place by a back-side approach (3), and this suggestion is discussed in connection with the known stereochemistry of olefin polymerization.Keywords: Ziegler–Natta, olefin polymerization, density functional.

ISSN:0008-4042    

DOI:10.1139/v95-122

出版商:NRC Research Press    

年代:1995

数据来源: NRC