Antimony-antimony bond formation by reductive elimination from a hafnium bis(stibido) complex

The bis(stibido) complex CpCp*Hf(SbMes2)2 (2) was prepared and structurally characterized. Complex 2 reacts with 2 equiv of xylylisocyanide to give the bis-insertion product CpCp*Hf[C(SbMes2)=N(2,6-MeC6H3)]2 (4). The reaction of 2 with oxidants (I2 and O2) or donors (carbon monoxide and diphenylacetylene) or thermolysis promotes the reductive elimination of Sb2Mes4.     

N-h and N-C bond activation of pyrimidinic nucleobases and nucleosides promoted by an osmium polyhydride

Complex OsH(6)(P(i)Pr(3))(2) (1) reacts with 1-methylthymine and 1-methyluracil to give OsH(3)(P(i)Pr(3))(2)(nucleobase') (2, 3) containing the deprotonated nucleobases (nucleobase') κ(2)-N,O coordinated by the nitrogen atom at position 3 and the oxygen bonded to the carbon atom of the ring at position 4. Similarly, the reactions of 1 with thymidine, 5-methyluridine, deoxyuridine, and uridine lead to OsH(3)(P(i)Pr(3))(2)(nucleoside') (4-7) with the deprotonated nucleoside (nucleoside') κ(2)-N,O coordinated by the nitrogen atom at position 3 and the oxygen bonded to the carbon atom at position 4 of the nucleobases. Treatment of complexes 5 and 7, containing nucleosides derived from ribose, with OsH(2)Cl(2)(P(i)Pr(3))(2) (8) in the presence of Et(3)N affords dinuclear species OsH(3)(P(i)Pr(3))(2)(nucleobase')-(ribose)(P(i)Pr(3))(2)H(2)Os (9, 10) formed by two different metal fragments. Complex 1 also promotes the cleavage of the N-C bond of 2-7 to give the dinuclear species {OsH(3)(P(i)Pr(3))(2)}(2)(nucleobase') (11, 12) with the nucleobase skeleton (nucleobase') κ(2)-N,O coordinated to both metal fragments. These compounds can be also prepared by reaction of 1 with 0.5 equiv of thymine and uracil. The use of 1:1 hexahydride:nucleobase molar ratios gives rise to the preferred formation of the mononuclear complexes OsH(3)(P(i)Pr(3))(2)(nucleobase') (13, 14; nucleobase' = monodeprotonated thymine or uracil). The X-ray structures of complexes 6, 11, and 14 are also reported.     

Carbon-nitrogen bond formation via the reaction of terminal alkynes with a dinuclear side-on dinitrogen complex

The dinuclear dinitrogen complex ([P2N2]Zr)2(mu-eta2:eta2-N2) reacts with terminal aryl alkynes to generate a new species in which the dinitrogen unit has been functionalized. The products formed have the general formula ([P2N2]Zr)2(mu-eta2:eta2-N2CCAr)(mu-CCAr) and display a styryl-hydrazido unit bridging the two Zr centers along with a bridging arylalkynide. The crystal structures of three of these products are reported. A mechanism is proposed for this process that involves cycloaddition of the alkyne to the side-on dinitrogen unit followed by protonation of the Zr-C bond by a second equivalent of terminal alkyne. A fluxional process is operative in solution that equilibrates the phosphorus nuclei at high temperature; in the slow exchange limit, the two [P2N2]Zr ends of complex are inequivalent as evidenced by four resonances in the 31P NMR spectrum for the inequivalent phosphorus donors. This C-N bond-forming reaction is unique in that an activated dinitrogen fragment undergoes a reaction with an alkyne.     

Complex formation of zirconium and hafnium with xylenol orange

The factors affecting the formation of zirconium and hafnium complexes of xylenol orange (XO) in perchloric acid have been examined. The optimum acid concentration for both systems is in the range 0.2–0.5 M HClO₄. When excess of metal is present, an initial complex with (XO) : metal ratio of 1 :1 is formed; this complex then undergoes an acid-dependent reaction, taking approximately 2 h to reach completion. Rate constants for this reaction have been determined. When excess of xylenol orange is present (i.e.(XO) : metal ? 2) a 2 :1 complex is formed which does not undergo further reaction. Extinction coefficients are given for the various complexes.     

Nitride formation by thermolysis of a kinetically stable niobium dinitrogen complex

The reduction of [P(2)N(2)]NbCl (where [P(2)N(2)] = PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh) with KC(8) under a dinitrogen atmosphere generates the paramagnetic dinuclear dinitrogen complex ([P(2)N(2)]Nb)(2)(mu-N(2)) (2). Complex 2 has been characterized crystallographically and by EPR spectroscopy. Variable-temperature magnetic susceptibility measurements indicate that 2 displays antiferromagnetic coupling between two Nb(IV) (d(1)) centers. A density functional theory calculation on the model complex [(PH(3))(2)(NH(2))(2)Nb](2)(mu-N(2)) was performed. Thermolysis of ([P(2)N(2)]Nb)(2)(mu-N(2)) in toluene generates the paramagnetic bridging nitride species where one N atom of the dinitrogen ligand inserts into the macrocycle backbone to form [P(2)N(2)]Nb(mu-N)Nb[PN(3)] (3) (where [PN(3)] = PhPMe(CHSiMe(2)NSiMe(2)CH(2)P(Ph)CH(2)SiMe(2)NSiMe(2)N)). Complex 3 has been characterized in the solid state as well as by variable-temperature magnetic susceptibility measurements. The reaction of ([P(2)N(2)]Nb)(2)(mu-N(2)) with phenylacetylene displaces the dinitrogen fragment to generate a paramagnetic eta(2)-alkyne complex, [P(2)N(2)]Nb(eta(2)-HCCPh) (4).     

C-C bond formation with carbon dioxide promoted by a silver catalyst

A catalytic amount of silver benzoate with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) was an effective catalytic system for the reaction of carbon dioxide with various ketones containing an alkyne group at an appropriate position. These reactions afforded the corresponding γ-lactone derivatives in good to high yields under mild conditions.     

Side-on bound dinitrogen complex of zirconium supported by a P2N2 macrocyclic ligand

Reduction of [P 2N 2]ZrCl 2 (where P 2N 2 = PhP(CH 2SiMe 2NSiMe 2CH 2) 2PPh) by KC 8 under N 2 generates the dinuclear dinitrogen complex ([P 2N 2]Zr) 2(mu-eta (2):eta (2)-N 2) and impurities in varying yields depending on the solvent and temperature. The toluene complex [P 2N 2]Zr(eta (6)-C 7H 8) along with a dinuclear species with bridging PC 6H 5 groups is observable. Also observable in the crude reaction mixtures is the mu-oxodiazenido derivative, ([P 2N 2]Zr) 2(mu-eta (2):eta (2)-N 2H 2)(mu-O), due to reaction with trace H 2O. This paper reports the full details of the preparation of ([P 2N 2]Zr) 2(mu-eta (2):eta (2)-N 2) including an improved method that involves reduction at low temperatures in a tetrahydrofuran solvent. Also reported is a reproducible synthesis of the oxodiazenido complex along with the X-ray structures of the dinitrogen complex and the oxodiazenido derivative.     

C-H bond activation and subsequent C-C bond formation promoted by osmium: 2-vinylpyridine-acetylene couplings

Complex OsH2Cl2(PiPr3)2 promotes the C-H activation of 2-vinylpyridine and subsequently couples the activated substrate with a second 2-vinylpyridine and two acetylene molecules. In the absence of 2-vinylpyridine, the activated substrate is coupled with an acetylene unit to afford a 2-butadienylpyridine derivative.     

Synthesis of a hafnocene disilene complex

Reaction of the magnesium transmetalation product of a 1,2-dipotassiodisilane with hafnocene dichloride gives a disilene hafnocene complex. X-ray crystallography of the respective trimethylphosphane adduct provides structural proof for this assignment.     

Interactions of hafnocene and zirconocene dihydrides with acetylenes. Synthesis of the first acetylene complex of hafnium

The first acetylene complex of hafnium, Cp₂Hf[Me₃SiC=CHf(H)Cp₂], was synthesized by the reaction of hafnocene dihydride Cp₂HfH₂ with bis(trimethylsilyl)acetylene in benzene. The reaction is accompanied by elimination of the Me₃Si group from the molecule of the initial acetylene, as a result of which the acetylenide derivative of hafnium Cp₂Hf(C=CSiMe₃)(H) acts as an acetylene ligand in the complex. Under analogous conditions, the reaction of zirconocene dihydride Cp₂ZrH₂ with bis(trimethylsilyl)acetylene affords an analogous acetylene complex of zirconium Cp₂Zr(M₃SiC=CZr(H)Cp₂]. Reactions of Cp₂HfH₂ with tolane and 3-hexyne proceed differently than the reaction with bis(trimethylsilyl)acetylene. Here the corresponding hafnacyclopentadiene metallacycles are the final products. For preliminary communication, see Ref. 3. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 853–856, April, 1997.     

Catalytic C-C bond cleavage and C-Si bond formation in the reaction of RCN with Et3SiH promoted by an iron complex

Catalytic C-C bond cleavage of acetonitrile and C-Si bond formation have been attained in the photoreaction of MeCN with Et3SiH in the presence of an iron complex, Cp(CO)2FeMe. This catalytic system can be applied for arylnitrile C-C bond cleavage.     

Chemical detection of zirconium and hafnium

Summary 3-Hydroxyflavone, morin and quercetin are suitable for the fluorescent detection of hafnium and zirconium under proper acidity and reagent concentration conditions. 3-Hydroxyflavone is the most sensitive reagent for both metals. Substantially acid solutions are preferred for the reactions of hafnium and zirconium to increase selectivity despite decreasing reaction sensitivity. The hydroxyflavone hafnium chelates are more stable to acid than the zirconium chelates especially with morin and quercetin. The very low background fluorescence of quercetin permits the detection of hafnium in strong perchloric acid where the fluorescence of the other two reagents hinders detection.

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Zusammenfassung 3-Hydroxyflavon(I), Morin(II) und Quercetin(III) eignen sich bei bestimmter Acidität und Reagenskonzentration zum Fluoreszenznachweis von Hafnium und Zirkonium. I ist das empfindlichste Reagens für beide Metalle. Deutlich saure Lösungen steigern die Selektivität der Reaktionen, setzen aber die Empfindlichkeit herab. Das Hafnium-I-Chelat ist gegenüber Säure stabiler als die Zirkoniumchelate, besonders von II und III. Die sehr geringe Untergrundfluoreszenz von III ermöglicht den Hafniumnachweis in starker Perchlorsäure, worin die Fluoreszenz der beiden anderen Reagenzien den Nachweis verhindert.

     

Electrochemical studies on organometallic compounds: XI. Electrogeneration of the zirconium(III) and hafnium(III) anions of zirconocene and hafnocene dichlorides

The one-electron reduction of zirconocene and hafnocene dichlorides Cp₂MCl₂ (M = Zr or Hf) yields the corresponding anion Cp₂MCl₂⁻. There is no cleavage of an MCl bond, in contrast to the result in the case of the analogous titanocene and vanadocene dichlorides.