Future prospects in organometallic chemisty of the Main Group metals: small molecules — supramolecular chemistry

Bulky alkyl ligands functionalised with N-donor groups of the type 2-C(SiMe₃)₂(6-R-2-pyridyl), R = H or Me, stabilise unusual bonding configurations, and lead into geminal bimetallic complexes, including the formation of a tetrametallic zinc cluster. This chemistry is poised for major advances in mixed metal complexes of the Main Group metals and beyond. Magnesium(anthracene)(THF)₃ and related complexes solve the ‘missing link’ in Grignard-reagent formation with the ability to routinely prepare Grignard reagents of benzylic halides. Future directions on the use of reactive metals in synthesis will adopt the principles of green chemistry, for example in the indium(0)-promoted reactions of organic halides with various functional groups in water. Supramolecular chemistry of o-carboranes in association with ‘rigid’ container and saddle-shape molecules has led to new classes of inclusion complexes of varying stoichiometry, and extension of this work into materials of higher complexity, with other carboranes and larger globular molecules, and with functionalised container molecules is a realisation.     

Ring-opening metathesis polymerization of norbornene and norbornadiene by tungsten(II) and molybdenum(II) complexes

The reaction of norbornene (NBE) and norbornadiene (NBD) in the presence of seven-coordinate tungsten(II) and molybdenum(II) complexes of the [(CO)₄M(μ-Cl)₃M(SnCl₃)(CO)₃] and [MCl(M′Cl₃)(CO)₃(NCMe)₂] (M=W, Mo; M′=Sn, Ge) types leads to ring-opening metathesis polymerization (ROMP) and to the formation of high molecular weight polymers. The geometric structure of these polymers was determined by means of ¹H- and ¹³C-NMR spectroscopy. The monitoring of the reaction between cyclic olefins and the metal complex by means of ¹H-NMR spectroscopy allowed us to observe the coordination of NBD to metal atoms in the initiation step of the polymerization process. Compounds of the [MCl(SnCl₃)(CO)₃(η⁴-NBD)] type prepared directly from [(CO)₄M(μ-Cl)₃M(SnCl₃)(CO)₃] or [MCl(M′Cl₃)(CO)₃(NCMe)₂] (M=W, Mo) in the presence of an excess of NBD initiate the ROMP reaction immediately. The detection of the first-formed products in the reaction between the metal complex and cyclic olefins provides valuable information concerning the nature of the initiating species.     

Substituted metal carbonyls XXIII . Syntheses of unicoordinated diphosphine complexes of Cr and Mo and their entry into heterobimetallics MM′(CO)10(μ-P-P) [M, M′= Cr, Mo, W; P---P = Ph2P(CH2)nPPh2, n = 2–4] as metalloligands

A series of pentacarbonyl complexes of chromium and molybdenum with unicoordinated-diphosphines, M(CO)₅(η¹-P-P) (P-P = dppe, dppp, dppb) has been prepared by amine oxide-induced phosphine substitution of the binary carbonyls. The basicity of the pendant phosphine groups was demonstrated by their ready conversion to the diphosphine-bridged heterobimetallic complexes (OC)₅M(μ-P-P)M′(CO)₅ (M, M′= Cr, Mo, W; M ≠ M′) in the presence of MCO)₅(CH₃CN). The complexes were characterized by IR and NMR (¹H and ³¹P-{¹H}) spectroscopy.     

Main Group and Group 11, 12, 2-pyridyl-(trimethylsilyl)methyl and -bis(trimethylsilyl)-methyl chemistry

Developments in the Main Group 1, 2, 13–15 and Groups 11 and 12 alkyl metal or metalloid chemistry of CH(SiMe₃)(2-pyridyl) (= r) and C(SiMe₃)₂(2-pyridyl) (= R) is reviewed along with observations on the closely related ligands, CH(SiMe₃)(6-methyl-2-pyridyl) (= rMe) and C(SiMe₃)₂(6-methyl-2-pyridyl) (= RMe).     

Recent studies on metal and metalloid bis(trimethylsilyl)methyls and the transformation of the bis(trimethylsilyl)methyl into the azaallyl and β-diketinimato ligands

Recent results (post-1990) on the synthesis and structures of bis(trimethylsilyl)methyls M(CHR₂)_m (R = SiMe₃) of metals and metalloids M are described, including those of the crystalline lipophilic [Na(μ-CHR₂)]_∞, [Rb(μ-CHR₂)(PMDETA)]₂, K₄(CHR₂)₄(PMDETA)₂, [Mg(CHR₂)(μ-CHR₂)]_∞, P(CHR₂)₂ (gaseous) and P₂(CHR₂)₄, [Yb(CHR₂)₂(OEt₂)₂] and [{Yb(CR₃)(μ-OEt)(OEt₂)}₂]; earlier information on other M(CHR₂)_m complexes and some of their adducts is tabulated. Treatment of M(CHR₂) (M = Li or K) with four different nitriles gave the X-ray-characterized azaallyls or β-diketinimates , and (LL′ = N(R)C(^tBu)CHR, L′L′ = N(R)C(Ph)C(H)C(Ph)NR, LL″ = N(R)C(Ph)NC(H)C(Ph)CHR, R = SiMe₃ and Ar = C₆H₃Me₂-2,5). The two lithium reagents were convenient sources of other metal azaallyls or β-diketinimates, including those of K, Co(II), Zr(IV), Sn(IV), Yb(II), Hf(IV) and U(VI)/U(III). Complexes having one or more of the bulky ligands [LL′]⁻, [L′L′]⁻, [LL]⁻, [LL″]⁻, [L″L]⁻, [LL]⁻ and [{N(R)C(^tBu)CH}₂C₆H₄-2]²⁻ are described and characterized (LL = N(H)C(Ph)C(H)C(Ph)NH, L″L = N(R)C(^tBu)C(H)C(Ph)NR, LL = N(R)C(^tBu)CHPh). Among the features of interest are (i) the contrasting tetrahedral or square-planar geometry for and , respectively, and (ii) olefin-polymerization catalytic activity of some of the zirconium(IV) chlorides.     

Thirty years of organometallic aryldiazenido arylazo derivatives

The aryldiazenido ligands provide the fourth member of the isoelectronic series CO, NO⁺, RNC, RN₂⁺ of ligands for transition metal complexes. The first aryldiazenido metal complex was reported in 1964 when p-CH₃OC₆H₄N₂Mo(CO)₂C₅H₅ was prepared by the reaction of NaMo(CO)₃C₅H₅ with p-CH₃OC₆H₄N₂⁺BF₄⁻. This review surveys the development of organometallic aryldiazenido chemistry since that time. Such organometallic aryldiazenido derivatives, including RN₂M(CO)₂C₅H₅, RN₂M(CO)₂(Pz₃BH) (M = Cr, Mo, W), [(η⁶-Me₆C₆)Cr(CO)₂N₂Ar]⁺, [(MeC₁₅H₄)M′(CO)₂N₂Ar]⁺ M′ = Mn, Re), [trans-PhN₂Fe(CO)₂(PPh₃)₂]⁺, and PhN₂M′(CO)₂(PPh₃)₂(PPh₃)₂ can be obtained by reactions of arenediazonium salts with suitably chosen transition metal nucleophiles. Analogous methods cannot be used to prepare alkyldiazenido transition metal complexes because of the instability of alkyldiazonium salts. However, the alkyldiazenido derivatives RCH₂N₂M(CO)₂C₅H₅ (R = H or Me₃Si) can be obtained from HM(CO)₃C₅H₅ and the corresponding diazoalkanes. Important aspects of the chemical reactivity of RN₂M(CO)₂Q derivatives (Q = C₅H₅, Pz₃BH) include CO substitution reactions, coordination of the second nitrogen in the RN₂ ligand to give heterobimetallic complexes such as C₅H₅Mo(CO)₂(μ-NNC₆H₄Me)(CO)₂C₅H₅, oxidative addition rections with X₂ X = Cl, Br, I), SnX₄, RSSR, and CINO, and reactions with further RN₂⁺ to give bis(aryldiazenido) derivatives (RN₂)₂MQL⁺ (L = CO, X⁻, etc.). Dearylation of an aryldiazenido ligand to a dinitrogen ligand can be effected by reaction of [(MeC₅H₄)M′(CO)₂N₂Ar]⁺ with certain nucleophiles to give (MeC₅H₄)M′(CO)₂N₂.     

Reactions of the sterically hindered organosilicon diol (Me3Si)2C(SiMe2OH)2 and some of its derivatives

The diol R₂C(SiMe₂OH)₂ (R = Me₃Si) has been shown to react with: SO₂Cl₂ to give R₂ Me₂; SOCl₂ to give R₂C(SiMe₂Cl)₂; Me₃SiI or Me₃SiCl to give R₂C(SiMe₂OSiMe₃)₂; R′COCl; (R′ = Me or CF₃) to give R₂C(SiMe₂O₂CR′)-(SiMe₂Cl); (R′CO)₂O (R′ = Me or CF₃ to give R₂C(SiMe₂O₂CR′)₂; with MeOH containing acid to give R₂C(SiMe₂OMe)₂; with neutral MeOH to give R₂C-(SiMe₂OMe)₂ and probably R₂ Me₂; MeLi to give R₂C(SiMe₂OLi)₂ (and the latter to react with PhMeSiF₂ to give R₂ Me₂). The diacetate R₂C(SiMe₂O₂CMe)₂ reacts with CsF in MeCN to give R₂C(SiMe₂F)₂; it does not react with NaN₃ or KSCN in MeCN, but the bis(trifluoroacetate) reacts with these salts with KOCN to give R₂C(SiMe₂X)₂ (X = N₃, NCS, NCO).     

Perfluoromethyl—element-liganden : XX. Bildung von heteronuclearen zweikernkomplexen des typs mm′(CO)nXY (M = Mn; M′ = Re, Co)

The reactions of MnRe(CO)₁₀ with As₂(CF₃)₄ and MnCo(CO)₉ with P₂(CF₃)₄, As₂(CF₃)₄, S₂(CF₃)₂, Se₂(CF₃)₂, (CF₃)₂EI (E = P, As), (CF₃)₂AsH, (CF₃)₂AsE′CF₃ (E′ = S, Se), (CF₃)₂PSeCF₃, Me₂AsI and (CF₃)₂PPMe₂, respectively, have been studied under various conditions. Besides already known mono- and binuclear compounds the heteronuclear complexes MnRe(CO)₈[As(CF₃)₂]₂ and MnCo(CO)₇[E(CF₃)₂]₂ (E = P, As) are formed. The reactions proceed via cleavage of the M---M′ bond and formation of the mononuclear species Mn(CO)₅X and M′(CO)_nY (M′ = Re, n = 5; M′ = Co, n = 4).     

Übergangsmetall-silyl-komplexe L. darstellung, struktur und reaktivität der Trihydrido-Silyl-und -Stannyl-Komplexe L3FeH3(ER3) (E =Si,

Photochemical reaction of (CO)₂(dppe)Fe(H)(SiR₃) with HSiR₃ (SiR₃ = Si(OMe)₃, Si(OEt)₃, SiMe₃, SiMe₂Ph, SiPh₃) yields the trihydrido silyl complexes (CO)(dppe)FeH₃(SiR₃ ). The analogous complexes (PR′Ph₂)₃ FeH₃(ER₃) are prepared by reaction of the H₂ -complexes (PR′Ph₂)₃FeH₂(H₂) with HER₃ (ER₃ = SiMe₃, SiMC₂Ph, SiMePh₂, SiPh₃, Si(Me₂)OSi(Me₂)H, SnPh₃, SnEt₃). Additional derivates of (CO) (dppe)FeH₃(SiR₃) (SiR₃ = SiMePh₂) and (PR′Ph₂)₃FeH₃(SiR₃) (SiR₃ = Si(OMe)₃, SiH₂Ph, SiHPh₂, Si(OEt)₃, SiMePhCl) are accessible by silane exchange starting from (CO)(dppe)FeH₃(SiMe₃) and (PR′Ph₂) ₃FeH₃(SiMe₃). (PBuPh₂)₃FeH₃(SiMePh₂) was also prepared from (PBuPh₂)₃FeH₂(N₂) and HSiMePh₂, and (PBuPh₂)₃FeH₃(SnMe₃) from (PBuPh₂)₃FeH₂(H₂) and Me₃SnCl. The complex (PBuPh₂) ₃FeH₃(SnMe₃) crystallizes as a toluene solvate in the cubic space group I 3d and shows crystallographically imposed C₃-symmetry. The complexes (CO)₂ (dppe)Fe(H)(SiR₃) and (PR′Ph₂)₃FeH₃(ER₃) are highly dynamic in solution. Low temperature NMR measurements and the E, Fe, H coupling constants strongly indicate that the exchange mechanism involves η²-HER₃ ligands.     

La-NMR-spektroskopie an allyllanthan(III)-komplexen

¹³⁹La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C₄H₈O₂)_3/2 [La(ν³-C₃H₅)₄], [Li(C₄H₈O₂)₂][Cp′_nLa(ν³-C₃]H₅)_4−n] (Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 and Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) and Li[R_nLa(ν³-C₃H₄)₄−n] (R = N(SiMe₃)₂; n = 1, 2 and R = CCsIMe₃; n = 4), as well as for neutral compounds for formulae La(ν³-C₃H₅)₃L_n (L = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_nLa(ν³-C₃H₅)_3−n (Cp′= Cp(ν⁵-Cp₅H₅), Cp *(ν⁵-C₅Me₅); n = 1, 2) and La(ν³-C₃H₂)₂X(THF)₂ X = Cl, Br, I). Typical ranges of the ¹³⁹La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum.

Zusammenfassung

¹³⁹La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung ]- [La)ν³-C₃H₅)₄, [Li(C₄H₈)₂][Cp′_nLa(ν³-C₃H₅)_4−n(Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 und Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) und Li[R_nLa(ν³-C₃H₅)_4−n (R = B(SiMe₃)₂; n = 1, 2 und R = CCSiMe₃; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν³-C₃H₅)₃L_n (L_n = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_n, La(ν³-C₃H₅)_3−n (Cp′ = Cp(ν⁵-C₅H₅), Cp * (ν⁵- Cp₅Me₅); n = 1, 2) und La(ν³-Cp₃H₅)₂X(THF)₂ (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt.     

High-performance liquid chromatography of the coordination isomers of triphenylphosphine-substituted homo- and hetero-bimetallic carbonyl complexes of manganese and rhenium

The isocratic normal-phase high-performance liquid chromatography of a series of triphenylphosphine (PPh₃)-substituted homo- and hetero-dinuclear metal carbonyl complexes [MM′ (CO)_10−n(PPh₃)_n, where M,M′ = Mn, Re; N = 1,2] is reported. A column packed with silica bonded with phenyl groups was used after preliminary experiments showed that columns packed with conventional silica, and with silica bonded with amion-cyano groups were unsatisfactory for separation. The mobile phases used were hexane-toluene (8:2) and hexane-dichloromethane (90:10). The results suggest that besides the symmetry-imposed polarity of the complexes, the nature of the metal and substituent ligand also determine their retention characteristics.     

Easily accessible and robust olefin-metathesis catalysts based on ruthenium vinylidene complexes

Nine mixed ligand ruthenium(II) vinylidene complexes with the general formula: [RuCl₂{=C=CHR′}(PCy₃)(L)] and [RuCl{=C=CHR′}(PCy₃)(sal-R)] (L=N-heterocyclic carbene, sal-R=salicylaldiminate anion, R′=Ph, SiMe₃, ^tBut) has been synthesized and characterized. These complexes are easily accessible from [RuCl₂(p-cymene)]₂, terminal alkynes, imidazolium salts or salicylaldimine salts and they have been found to serve as good catalyst precursors for ring-opening metathesis polymerization (ROMP) of norbornene, substituted norbornenes, polycyclic alkenes and cyclooctene and ring-closing metathesis (RCM) of ,ω-dienes. Furthermore, these precursors possess extremely high stability toward air, heat and moisture in comparison with other metathesis-active alkylidene ruthenium systems. No significant catalyst decomposition was found for several days at elevated temperatures.     

Redox potential, ligand and structural effects in rhodium(I) complexes

The electrochemical behaviour of the set of tetracoordinate rhodium(I) complexes [Rh(O^∩O)(CO)L] [O^∩O=MeC(O)CHC(O)Me (acac), L=CO (1), P(NC₄H₄)₃ (2), PPh(NC₄H₄)₂ (3), PPh₂(NC₄H₄) (4), PPh₃ (5), PCy₃ (6), P(OPh)₃ (7) or PPh₂(C₆H₄OMe-4) (8); O^∩O=PhC(O)CHC(O)Me (bac), L=CO (9) or PPh₃ (10); O^∩O=PhC(O)CHC(O)CF₃(bta), L=CO (11) or PPh₃ (12)] and of the pentacoordinate [RhH(CO)L₃] [L=P(NC₄H₄)₃ (13), PPh₃ (14), P(OPh)₃ (15) or P(OC₆H₄Me-4)₃ (16)] and [RhHL₄] [L=PPh₃ (17) or P(OC₆H₄Me-3)₃ (18)] was studied by cyclic voltammetry and controlled potential electrolysis, in aprotic medium, at a Pt electrode. They present a single-electron oxidation wave (I) (irreversible or quasi-reversible) that can be followed, at a higher potential, by a second and irreversible one (II). The values of first oxidation potential for the tetracoordinate complexes fit the additive Lever's electrochemical parameterisation, and the ligand electrochemical Lever E_L and Pickett P_L parameters were estimated for the N-pyrrolyl phosphines PPh_n(NC₄H₄)_3−n (n=0, 1 or 2) and for the organophosphines PCy₃ and PPh₂(C₆H₄OMe-4), the former behaving as weaker net electron donors (the electron donor ability decreases with the increase of the number of N-pyrrolyl groups) than the latter phosphines. The pentacoordinate hydride complexes 13–18 fit a distinct relationship which enabled the estimate of the E_L ligand parameter for the phosphites P(OC₆H₄Me-3)₃ and P(OC₆H₄Me-4)₃. Electrochemical metal site parameters were obtained for the square planar and the pentacoordinate Rh(I)/Rh(II) couples and, for the former, the redox potential is shown to present a much higher sensitivity to a change of a ligand than the octahedral redox couples investigated so far. Linear relationships were also observed between the oxidation potential and the P_L ligand parameter (for the series [Rh(acac)(CO)L]) or the infrared ν(CO) frequency, and a generalisation of the former type of correlation is proposed for series of square-planar 16-electron complexes [M′_SL] with a common 14-electron T-shaped binding metal centre {M′_S}. Oxidation of 5 by Ag[PF₆] leads to the dimerisation of the derived Rh(II) species.     

Ab initio and DFT computer studies of complexes of trimethylphosphine and products of substituted phosphonium cations with hydroxide, chloride and fluoride anions: Phosphorus analogues of choline and acetylcholine

Theoretical calculations (DFT, MP2) are reported for up to four sets of reaction products of trimethylphosphine, (CH₃)₃P, each with H₂O, HCl and HF together with DFT calculations on up to three sets of reaction products of substituted phosphonium cations, (CH₃)₃P–R⁺. These products comprise (a) P(III) normal complexes (CH₃)₃PHY, (b) P(IV) ‘reverse’ complexes Y(H–CH₂)₃P–R, (c) P(IV) ylidic complexes YHCH₂(CH₃)₂P–R and (d) P(V) covalent compounds Y–P(CH₃)₃–R for Y=HO, Cl and F and R=H, CH₃, C₂H₅, C₂H₄OH and C₂H₄OC:OCH₃. Calculations are carried out at the B3LYP/6-31+G(d,p) level in all cases and also at the MP2/6-31+G(d,p) level for systems in which R=H. Minimum energy structures are determined for predicted complexes or structures and geometrical properties, harmonic vibrations and BSSE corrected binding energies are reported and compared with the limited experimental information available. Potential energy scans predict equilibria between covalent trigonal bipyramidal P(V) forms and reverse complexes comprising hydrogen bonded or ion pair, tetrahedral P(IV) forms separated by low potential energy barriers. Similar scans are also reported for equilibria between reverse complexes and ylidic complexes for Y=OH and R=CH₃, C₂H₅, C₂H₄OH and C₂H₄OC:OCH₃. Corrected binding energies, structures and values of harmonic modes are discussed in relation to bonding The names ‘pholine’ and ‘acetylpholine’ are suggested for phosphorus analogues to choline and acetylcholine.     

Substituted cyclopentadienyl ligands—10. Intramolecular steric interactions in [(η-C5H3(SiMe3)2)Mo(CO)2(L)I]

Reaction of C₅H₄(SiMe₃)₂ with Mo(CO)₆ yielded [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₃]₂, which on addition of iodine gave [(η⁵-C₅H₃(SiMe₃)₂Mo(CO)₃I]. Carbonyl displacement by a range of ligands: [L = P(OMe)₃, P(OPrⁱ)₃,P(O-o-tol)₃, PMe₃, PMe₂Ph, PMePh₂, PPh₃, P(m-tol)₃] gave the new complexes [(η⁵-C₅H₃(SiMe₃)₂ MO(CO)₂(L)I]. For all the trans isomer was the dominant, if not exclusive, isomer formed in the reaction. An NOE spectral analysis of [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₂(L)I] L = PMe₂Ph, P(OMe)₃] revealed that the L group resided on the sterically uncongested side of the cyclopentadienyl ligand and that the ligand did not access the congested side of the molecule. Quantification of this phenomenon [L = P(OMe)₃] was achieved by means of the vertex angle of overlap methodology. This methodology revealed a steric preference with the trans isomer (less congestion of CO than I with an SiMe₃ group) being the more stable isomer for L = P(OMe)₃.     

Electrochemical behaviour of some polyoxo clusters

We describe the redox behaviour in non-aqueous solvents of some cyclopentadienyl(oxo)titanium derivatives. The derivative [Ti₄{η⁵-C₅H₄(SiMe₃)}₄(μ-O)₆] shows an electrochemically and chemically reversible le reduction process, followed by a multi-electron, chemically complicated reduction at a fairly cathodic potential. On the basis of the overall electrochemical features and the comparison with the redox behaviour of the quasi-planar compound [[Ti{η⁵-C₅H₄(SiMe₃)}Cl(μ-O)]₄] we propose an EECCEE mechanism for the first derivative, where the second electron-transfer induces a cascade of chemical reactions giving rise to irreversible cluster breakdown. The electrochemically induced fragmentation can be viewed as a retrosynthetic pathway. The heterometallic derivative [{Ti(η⁵-C₅H₄Me)₂(μ₂-MoO₄)₂}₂] shows two consecutive reduction processes; the first is chemically reversible, and the second quasi-reversible. The molybdate bridges apparently increase the stability of the electrogenerated anions. However none of these poly-oxo clusters can be considered as good models of electron ‘sinks’.     

Acyl complexes of molybdenum: structural and reactivity studies

The following structural peculiarities of the agostic acyl structure ₂R) (R = H, SiMe₃) and some characteristic chemical reactivity of the M-η²-acyl and iminoacyl linkage are described. (i) A structural comparison of the bonding parameters within three agostic acetyl Mo complexes containing the dithioacid ligand, indicates that the agostic interaction strengthens upon increasing the electron-releasing properties of the S-chelating ligand. (ii) The acyl-xanthate complex Mo(C(O)Me)(S₂COR)(CO)(PMe₃)₂ undergoes loss of a sulfur atom from the coordinated xanthate and coupling with the acyl ligand to form complexes containing coordinated alkoxythiocarbonyl and monothioacetate ligands. The latter can be metathetically replaced by KS₂COR. (iii) Upon heating at 70°C η²-acyl-dicarbonyl bispirazolilborate complexes of molybdenum of the type Mo(H₂B(pz^*)₂)(η²-C(O)Me)(CO)₂(PMe₃) (pz^* = 3,5-dimethyl-pyrazol-1-yl) yield functionalized acyl ligands derived from the stereo- and regioselective intramolecular addition of one of the B---H bonds of the H₂B(pz^*)₂ group across the C=O moiety of the η²-acyl group. (iv) The η²-acyl-isocyanide complexes {Mo}(η²-C(O)R)(CNR′) ({Mo} = Mo(H₂B(pz^*)₂)(CO)(PMe₃)) undergo irreversible thermal isomerization to the corresponding η²-iminoacyl-carbonyl derivatives {MO}(η²-C(NR′)R)(CO). This isomerization reaction follows first-order kinetics.     

Synthesis and chemistry of the bis(trimethylsilyl)amido bis-tetrahydrofuranates of the group 2 metals magnesium, calcium, strontium and barium. X-ray crystal structures of Mg[N(SiMe3)2]2·2THF and related Mn[N(SiMe3)2]2·2THF

Transamination reactions utilizing the compound mercuric bis(trimethylsilyl)amide, Hg{N(SiMe₃)₂}₂, in tetrahydrofuran (THF), and the metals Na, Mg, Ca, Sr, Ba and Al have been investigated. Thus the THF solvated compounds Na[N(SiMe₃)₂]·THF and M[N(SiMe₃)₂]₂·2THF, M = Mg, Ca, Sr and Ba (1–4), have been prepared. The X-ray crystal structures of 1 and the related manganese compound Mn[N(SiMe₃)₂]₂·2THF (5) are reported. Interaction of the silylamides, 2–4, with a range of crown ethers apparently proceeded with elimination of silylamine, (Me₃Si)₂NH, and novel ring opening of the crown ethers, generating species containing a donor alkoxide ligand with a vinyl ether function, presumably, ---O(CH₂CH₂O)_nCH=CH₂ (n = 3−5). The silylamides 2–4 were also cleanly converted to the corresponding alkoxides (from ¹H NMR data) in reactions with stoichiometric quantities of 3-ethyl-3-pentanol.     

Zur chemie des galliums, 6: Tris(trimethylsilyl) silylgallium(I) —eine experimentelle und theoretische studie

The gallium(I)tris(trimethylsilyl)silyl compound {GaSi(SiMe₃)₃}₄ (1) is obtained by reaction of Ga₂Cl₄-2dioxane with LiSi(SiMe₃)₃-3THF. The crystal structure of 1 reveals a tetramer with a nearly regular tetrahedral framework of gallium atoms. The gallium-gallium distances average 258.4 pm. Ab initio calculations on various substituted gallium tetrahedrons showed a greater stability of silyl-substituted cages compared with organyl substituted ones. Crystal data, with Mo K radiation are as follows: {GaSi(SiMe₃)₃}₄ · Si(SiMe₃) ₄ (1), a, B = 1923.3(3) pm, C = 2671.2(4) pm, V = 9.881(3) nm³; tetragonal space group P4/ncc; Z = 4; 1513 ( I > 2σ(I)) data; RI = 0.068.

Zusammenfassung

Das Gallium(I)tris(trimethylsilyl)silyl-Derivat {GaSi(SiMe₃)₃}₄ (1) wird durch Umsetzung von Ga₂Cl₄-2Dioxan mit LiSi(SiMe₃)₃-3THF erhalten. Die Analyse der Kristallstruktur zeigt ein Tetramer mit einem nahezu regulären Gallium-Tetraeder-Gerüst. Der Mittelwert der Gallium-Gallium-Abstände betrügt 258.4 pm. Ab initio-Berechnungen verschiedener Gallium(I)-Verbindungen belegten eine erhöhte Stabilität von silyl-substituierten Clustern im Vergleich zu organyl-substituierten. Kristalldaten, mit Mo K -Strahlung; {GaSi(SiMe₃)₃ }₄ · Si(SiMe₃)₄ (1), a, B = 1923.3(3) pm, C = 2671.2(4) pm, V = 9.881(3) nm³; tetragonal, Raumgruppe P4/ncc; Z = 4; 1513 (I > 2 σ(I)) Daten; RI = 0.068.     

Copper(I) and mercury(II) halide complexes of 1,2-bis(diphenylthioylphosphino)hydrazine

The reaction of 1,2-bis(diphenylthioylphosphino)hydrazine (L) with copper(I) and mercury(II) halides affords the complexes, [{CuLX}₂] (X = I, Br or Cl), [HgLX₂] (X = Cl or Br) and the tetrametallic complex, [{L(HgI₂)₂}₂]. Single crystal X-ray structures have been performed on the uncoordinated ligand, L, as well as the complexes [{CuLX}₂] (X = I, Br and Cl), [HgLBr₂] and [{L(HgI₂)₂}₂. The molecules of L exist as dimers as a result of pairs of N–HS hydrogen bonds. The copper(I) complexes are centrosymmetric dimetallic species, the two copper atoms being bridged by L and the X atoms. In all cases the coordination sphere around the Cu atoms is approximately trigonal pyramidal with an ‘S₂X₂’ donor set. The complex, [HgLBr₂], is a distorted tetrahedral monomer with an ‘S₂Br₂’ donor set and L acting as a bidentate thus forming a seven-membered chelate ring. The tetramercury iodo complex, [{L(HgI₂)₂}₂], contains two ‘L(HgI₂)₂’ units linked centrosymmetrically via an I atom from each moiety. The geometry around the Hg atoms is distorted tetrahedral. The influence of hydrogen bonding between the hydrazine backbone hydrogens of L and the coordinated halide ions in for the structures of the metal complexes is discussed.