Reductive degradation of nido-1-CB8H12 into smaller-cage carborane systems via new monocarbaboranes [arachno-5-CB8H13](-) and closo-2-CB6H8

Treatment of the nido-1-CB8H12 (1) carborane with NaBH4 in THF at ambient temperature led to the isolation of the stable [arachno-5-CB8H13]- (2(-)), which was isolated as Na+[5-CB8H13]-.1.5 THF and PPh4 +[5-CB8H13]- in almost quantitative yield. Compound 2(-) underwent a boron-degradation reaction with concentrated hydrochloric acid to afford the arachno-4-CB7H13 (3) carborane in 70 % yield, whereas reaction between 2(-) and excess phenyl acetylene in refluxing THF gave the [closo-2-CB6H7]- (4-) in 66 % yield. Protonation of the Cs+4(-) salt with concentrated H2SO4 or CF3COOH in CH2Cl2 afforded a new, highly volatile 2-CB6H8 (4) carborane in 95 % yield, the deprotonation of which with Et3N in CH2Cl2 leads quantitatively to Et3NH+[2-CB6H7](-) (Et3NH+4(-)). Both compounds 4- and 4 can be deboronated through treatment with concentrated hydrochloric acid in CH2Cl2 to yield the carbahexaborane nido-2-CB5H9 (5) in 60 % yield. New compounds 2-, 3, and 4 were structurally characterised by the ab initio/GIAO/MP2/NMR method. The method gave superior results to those carried out using GIAO-HF when relating the calculated 11B NMR chemical shifts to experimental data.     

Synthesis of the arachno-4-CB(8)H(12)(2)(-) monocarbaborane dianion and NMR/computational studies of the fluxional processes observed in the isoelectronic nine-vertex arachno anions: arachno-4-CB(8)H(12)(2)(-), arachno-4-CB(8)H(13)(-), and arachno-4-SB(8)H(11)(-)

The new monocarbaborane dianion, arachno-4-CB(8)H(12)(2)(-) has been synthesized from the reaction of arachno-4-CB(8)H(14) with 2 equiv of NaH in polar solvents. DFT/GIAO computations at the B3LYP/6-311G//B3LYP/6-311G level, in conjunction with 1D and 2D NMR spectroscopic studies, have confirmed that the dianion results from deprotonation of both the endo-CH and one bridging hydrogen of the parent arachno-4-CB(8)H(14). While the DFT calculations indicate that a C(1) symmetric structure is lowest in energy, the experimental solution NMR data are consistent with the dianion having a C(s)() symmetric structure, thus suggesting that it is fluxional in solution. Transition state calculations located a low-energy pathway with an activation energy of only 2.7 kcal/mol that allows the migration of the bridging hydrogen between the two enantiomeric forms of the dianion. The process can occur by a single-step, simple rotation through a transition state structure containing a -BH(2) group at the B7 boron. Averaging the calculated (11)B NMR chemical shifts of the resonances for those atoms in the static enantiomeric structures that become equivalent by this fluxional process then gives excellent agreement with the solution NMR data. Transition state calculations of the fluxional behavior previously observed for the isoelectronic arachno-4-CB(8)H(13)(-) and arachno-4-SB(8)H(11)(-) monoanions have likewise revealed related low-energy (0.3 and 5.0 kcal/mol, respectively) rearrangement mechanisms involving the simultaneous rotation of three hydrogens (two bridging and one -BH(2)) through a C(s)() symmetry transition state containing three -BH(2) groups.     

PtII-mediated 1,3-dipolar cycloaddition of oxazoline N-oxides to nitriles as a key step to dihydrooxazolo-1,2,4-oxadiazoles

A novel type of heterocycle, viz., 2,3a-disubstituted 5,6-dihydro-3aH-[1,3]oxazolo[3,2-b][1,2,4]oxadiazoles, was generated by an intermolecular PtII-mediated 1,3-dipolar cycloaddition (1,3-DCA) between the oxazoline N-oxide C(Me)2CH2OC(R)=N+(O-) (R = Me, Et) and coordinated nitriles in the complexes trans/cis-[PtCl2(R'CN)2] [R' = Me, Et, CH2Ph, Ph, N(C5H10)]. The reaction is unknown for free RCN and oxazoline N-oxides, but under PtII-mediated conditions, it proceeds smoothly (CH2Cl2, 20-25 degrees C, 18-20 h) and gives pure complexes [PtCl2{N=C(R')ONC(R)OCH2CMe2}2] [R/R' = Me/Me, 1; Me/Et, 2; Me/CH2Ph, 3; Me/Ph, 4; Me/N(C5H10), 5; Et/Me, 6; Et/Et, 7; Et/CH2Ph, 8; Et/Ph, 9; Et/N(C5H10), 10] in 42-84% yields after column chromatography. Compounds 1-10 were characterized by elemental analyses (C, H, N), FAB+-MS, IR, and 1H and 13C{1H} NMR spectroscopies, and X-ray diffraction (for 1, 2, 5, and 9). With the exception of benzonitrile complexes, 1,3-DCA of oxazoline N-oxides to the PtII-ligated nitriles occurred diastereoselectively and afforded mixtures of enantiomers. Depending on the substituents on nitriles, asymmetric atoms in both of the formed heterocyclic ligands have the same (SS/RR) or different (SR/RS) configurations. The heterocyclic ligands were liberated from 1-4 and 6-9 by treatment with excess ethane-1,2-diamine (en) in CH2Cl2 for 1 day at 20-25 degrees C (for R' = Me, Et, CH2Ph) and at 50 degrees C (for R' = Ph) to achieve the free organic species and the well-known [Pt(en)2](Cl)2; the products were separated, and 2,3a-disubstituted 5,6-dihydro-3aH-[1,3]oxazolo[3,2-b][1,2,4]oxadiazoles (11-18) were characterized by ESI+-MS and 1H and 13C{1H} NMR spectroscopies.     

Quenched gas-phase reactions of tetraborane(10), B4H10, with substituted alkynes: new nido-dicarbapentaboranes and arachno-monocarbapentaboranes

New alkyl derivatives of the nido-dicarbapentaborane, 1,2-C(2)B(3)H(7), and arachno-carbapentaborane, 1-CB(4)H(10), have been identified as the main volatile carbaborane products in quenched gas-phase reactions of tetraborane(10), B(4)H(10), with alkyl-substituted ethynes RC[triple bond]CR' (R = Me, Et, (n)Pr or (t)Bu, R' = H; R = Me or Et, R' = Me). The gaseous mixtures were heated at 70 degrees C, and monitored by gas-phase mass spectrometry. Each reaction was quenched when the ethyne was used up. The quenched gas-phase reaction of B(4)H(10) and Me(3)SiC[triple bond]CH gave a single volatile carbaborane product, 1-Me(3)Si-1,2-C(2)B(3)H(6).     

Nitrile-amidine coupling at Pt(IV) and Pt(II) centers. An easy entry to imidoylamidine complexes

Treatment of trans-[PtCl4(RCN)2] (R = Me, Et, Ph, NEt2) with 2 equiv of the amidine PhC(=NH)NHPh in a suspension of MeCN (R = Me), CHCl3 (R = Et, Ph), or in CHCl3 solution (R = NEt2) results in the formation of the imidoylamidine complexes trans-[PtCl4{NH=C(R)N=C(Ph)NHPh}2] (1-4) isolated in good yields (66-84%). The reaction of soluble complexes 3 and 4 with 2 equiv of Ph3P=CHCO2Me in CH2Cl2 (40 degrees C, 5 h) leads to dehydrochlorination resulting in a chelate ring closure to furnish the platinum(IV) chelates [PtCl2{NH=C(R)NC(Ph)=NPh}2] (R = Ph, 5; R = NEt2, 6), accordingly, and the phosphonium salt [Ph3PCH2CO2Me]Cl. Treatment of 5 with 3 equiv of Ph3P=CHCO2Me at 50 degrees C for 5 d resulted in only a 30% conversion to the corresponding Pt(II) complex [Pt{NH=C(NEt2)NC(Ph)=NPh}2] (15). The reduction can be achieved within several minutes, when Ph2PCH2CH2PPh2 in CDCl3 is used. When the platinum(II) complex trans-[PtCl2(RCN)2] is reacted with 2 equiv of the amidine, the imidoylamidinato complexes [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) and [PhC(=NH)NHPh] x HCl (7) are formed. The reaction of trans-[PtCl2(RCN)2] with 4 equiv of the amidine under a prolonged reaction time or treatment of [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) with 2 more equiv of the amidine yields the complex bearing two chelate rings [Pt{NH=C(R)NC(Ph)=NHPh}2] (12-15). The treatment of cis-[PtCl2(RCN)2] (R = Me, Et) with the amidine gives ca. 50-60% yield of [PtCl2{NH=C(R)NHC(Ph)=NHPh}] (16 and 17). All of the platinum compounds were characterized by elemental analyses; FAB mass spectrometry; IR spectroscopy; 1H, 13C{1H}, and 195Pt NMR spectroscopies, and four of them (4, 6, 8, and 15) were also characterized by X-ray crystallography. The coupling of the Pt-bound nitriles and the amidine is metal-mediated insofar as RCN and PhC(=NH)NHPh do not react in the absence of the metal centers in conditions more drastic than those of the observed reactions. The nitrile-amidine coupling reported in this work constitutes a route to the synthesis of imidoylamidine complexes, some of them exhibiting luminescent properties.     

The first member of the eleven-vertex azadicarbaborane series, 1,6,9-NC2B8H13, and its N-alkyl derivatives

Reactions between closo-1,2-C(2)B(8)H(10) (1) and amines of general formulation R(1)R(2)NH (where R(1), R(2) = H, H; Me, H; t-Bu, H and Et, Et) resulted in a straightforward cluster expansion and formation of the 11-vertex arachno-azadicarbaboranes of the 1,1-R(1),R(2-)1,6,9-NC(2)B(8)H(11) (2) cluster constitution (where R(1), R(2) = H, H 2a; Me, H 2b; t-Bu, H 2c and Et, Et 2d) in yields 10-75%, depending on the nature of the amine used. The reactions are the first example of a direct closo to arachno transformation in the area of cluster-boron compounds. Compounds 2b and 2c were isolated in two isomeric forms anti- and syn- that differ in the positioning of the t-Bu substituent with respect to the bridging hydrogen site. Deprotonation of compounds 2 generally leads to removal of the bridging proton and formation of the [1,1-R(1),R(2-)1,6,9-NC(2)B(8)H(11)](-) (2-) anions that, in the case of the monoalkylated Me and t-Bu derivatives, adopt only an anti configuration. The structure of anti-2c was determined by X-ray diffraction analysis and the geometries of the parent compound and the corresponding syn and anti isomers were optimised at the RMP2/6-31G* level. The composition of all compounds is consistent with the results of mass spectrometry and multinuclear ((1)H and (11)B) spectroscopy complemented by two-dimensional [(11)B-(11)B]-COSY and (1)H{(11)B(selective)} NMR measurements. Experimental (11)B chemical shifts generally show acceptable agreement with theoretical values calculated by GIAO methods, in particular at GIAO-MP2/II, where possible.     

The metalla-Pinner reaction between Pt(IV)-bound nitriles and alkylated oxamic and oximic forms of hydroxamic acids

The nitrile ligands in the platinum(IV) complexes trans-[PtCl4(RCN)2] (R=Me, Et, CH2Ph) and cis/trans-[PtCl4(MeCN)(Me2SO)] are involved in a metalla-Pinner reaction with N-methylbenzohydroxamic acid (N-alkylated form of hydroxamic acid, hydroxamic form; F1), PhC(=O)N(Me)OH, to achieve the imino species [PtCl4[NH=C(R)ON(Me)C(=O)Ph]2 (1-3) and [PtCl4[NH=C(Me)ON(Me)C(=O)Ph](Me2SO)] (7), respectively. Treatment of trans-[PtCl4(RCN)2] (R=Me, Et) and cis/trans-[PtCl4(MeCN)(Me2SO)] with the O-alkylated form of a hydroxamic acid (hydroximic form), i.e. methyl 2,4,6-trimethylbenzohydroximate, 2,4,6-(Me3C6H2)C(OMe)=NOH (F2A), allows the isolation of [PtCl4[NH=C(R)ON=C(OMe)(2,4,6-Me3C6H2)]2] (5, 6) and [PtCl4[NH=C(Me)ON=C(OMe)(2,4,6-Me3C6H2)](Me2SO)] (8), correspondingly. In accord with the latter reaction, the coupling of nitriles in trans-[PtCl4(EtCN)2] with methyl benzohydroximate, PhC(OMe)=NOH (F2B), gives [PtCl4[NH=C(Et)ON=C(OMe)Ph]2] (4). The addition proceeds faster with the hydroximic F2, rather than with the hydroxamic form F1. The complexes 1-8 were characterized by C, H, N elemental analyses, FAB+ mass-spectrometry, IR, 1H and 13C[1H] NMR spectroscopies. The X-ray structure determinations have been performed for both hydroxamic and hydroximic complexes, i.e. 2 and 6, indicating that the imino ligands are mutually trans and they are in the E-configuration.     

Aluminacyclopropene: syntheses, characterization, and reactivity toward terminal alkynes

Reactions of LAl with ethyne, mono- and disubstituted alkynes, and diyne to aluminacyclopropene LAl[eta2-C2(R1)(R2)] ((L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3); R1 = R2 = H, (1); R1 = H, R2 = Ph, (2); R1 = R2 = Me, (3); R1 = SiMe3, R2 = C[triple bond]CSiMe3, (4)) are reported. Compounds 1 and 2 were obtained in equimolar quantities of the starting materials at low temperature. The amount of C2H2 was controlled by removing an excess of C2H2 in the range from -78 to -50 degrees C. Compound 4 can be alternatively prepared by the substitution reaction of LAl[eta2-C2(SiMe3)2] with Me3SiC[triple bond]CC[triple bond]CSiMe3 or by the reductive coupling reaction of LAlI2 with potassium in the presence of Me3SiC[triple bond]CC[triple bond]CSiMe3. The reaction of LAl with excess C2H2 and PhC[triple bond]CH (<1:2) afforded the respective alkenylalkynylaluminum compounds LAl(CH=CH2)(C[triple bond]CH) (5) and LAl(CH=CHPh)(C[triple bond]CPh) (6). The reaction of LAl(eta2-C2Ph2) with C2H2 and PhC[triple bond]CH yielded LAl(CPh=CHPh)(C[triple bond]CH) (7) and LAl(CPh=CHPh)(C[triple bond]CPh) (8), respectively. Rationally, the formation of 5 (or 6) may proceed through the corresponding precursor 1 (or 2). The theoretical studies based on DFT calculations show that an interaction between the Al(I) center and the C[triple bond]C unit needs almost no activation energy. Within the AlC2 ring the computational Al-C bond order of ca. 1 suggests an Al-C sigma bond and therefore less pi electron delocalization over the AlC2 ring. The computed Al-eta2-C2 bond dissociation energies (155-82.6 kJ/mol) indicate a remarkable reactivity of aluminacyclopropene species. Finally, the 1H NMR spectroscopy monitored reaction of LAl(eta2-C2Ph2) and PhC[triple bond]CH in toluene-d8 may reveal an acetylenic hydrogen migration process.     

Hafnocene catalysts for selective propylene oligomerization: efficient synthesis of 4-methyl-1-pentene by beta-methyl transfer

A series of hafnocene complexes (eta5-C5Me4R1)(eta5-C5Me4R2)HfCl2 with [R1, R2] = [H, H] (1), [Me, H] (2), [Me, Me] (3), [Et, Me] (4), [(i)Pr, Me] (5), [SiMe(3), Me] (6), [(t)Bu, Me] (7), [(n)Bu, Me] (8), [(i)Bu, Me] (9), [Et, Et] (10), [(n)Bu, (n)Bu] (11), [(i)Bu, (i)Bu] (12) was tested as catalyst precursors for propylene oligomerization. Upon activation with methylaluminoxane or [Ph(3)C][B(C(6)F(5))(4)]/Al(i)Bu(3), complexes 2-4 and 8-12 catalyzed the dimerization of propylene to produce 4-methyl-1-pentene with selectivities ranging from 23.9 to 61.6 wt % in the product mixture. The selectivity was dependent on the nature of the substituents R(1) and R(2), with the highest value found for (eta5-C5Me4(i)Bu)2HfCl2 (12). Rapid deactivation was observed for 5-7, whereas (eta5-C5Me4H)2HfCl2 (1) polymerized propylene. 4-Methyl-1-pentene is proposed to form by repeated 1,2-insertion of propylene into the hafnocene methyl cation, followed by selective beta-methyl elimination. Detailed analysis of the byproduct distribution (isobutene, 1-pentene, 2-methyl-1-pentene, 2,4-dimethyl-1-pentene, 4-methyl-1-heptene, 4,6-dimethyl-1-heptene), determined by gas chromatography, was performed with the aid of a stochastic simulation involving rate constants for the propagation by insertion, beta-hydride elimination, and beta-methyl elimination. The rate of termination is dependent on the structure of the growing chain of the active species as well as on the bulkiness of the cyclopentadienyl ligands. The selectivity highly depends on the reaction conditions (pressure, temperature, concentration of methylaluminoxane). The rates of beta-methyl elimination leading to 4-methyl-1-pentene were proportional to propylene pressure for 2-4 and 8-10 but practically independent from propylene pressure for the sterically bulkier derivatives 11-12.     

Syntheses, characterizations, and coordination chemistry of the 10-vertex phosphadicarbaboranes 6-R-arachno-6,8,9-PC2B7H11 and 6-R-arachno-6,5,7-PC2B7H11

The 10-vertex phosphadicarbaboranes, 6-R-arachno-6,8,9-PC(2)B(7)H(11) (1) (R = Ph 1a or Me 1b) and 6-R-arachno-6,5,7-PC(2)B(7)H(11) (2) (R = Ph 2a or Me 2b) have been synthesized using in situ dehydrohalogenation reactions of RPCl(2) (R = Ph or Me) with the arachno-4,5-C(2)B(7)H(13) and arachno-4,6-C(2)B(7)H(13) carboranes, respectively. X-ray crystallographic determinations in conjunction with DFT/GIAO/NMR calculations and NMR spectroscopic studies have established that both 1 and 2 have open cage structures based on an icosahedron missing two vertexes. The two isomeric compounds differ in the positions of the carbons and bridging hydrogens on the open face. Studies of the reactions of 2a with BH(3).THF, S(8), and hydrogen peroxide demonstrated that 2a shows strong donor properties yielding the compounds endo-6-H(3)B-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (3), endo-6-S-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (4), and endo-6-O-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (5) in which the BH(3), S, and O substitutents are bonded to an electron lone pair localized at the phosphorus endo-position. The reaction of 2a with an excess of S(8) results in the loss of a framework boron to produce the unique open-cage compound micro(7,8)-[HS(Ph)P]-hypho-7,8-C(2)B(6)H(11) (6). 2a also formed the donor complexes cis-(eta(1)-[6-Ph-arachno-6,5,7-PC(2)B(7)H(11)])(2)PtBr(2) (7) and trans-(eta(1)-[6-Ph-arachno-6,5,7-PC(2)B(7)H(11)])(2)PdBr(2) (8) in which the metal fragment is bonded in an eta(1)-fashion at the phosphorus endo-position. In these complexes, 2a is functioning as a two-electron sigma donor to the metals and can thus be considered as an analogue of the PR(3) ligands in the classical cis-(PPh(3))(2)PtBr(2) and trans-(PPh(3))(2)PdBr(2) coordination complexes. Although 1a did not show the donor properties exhibited by 2a, its dianion 6-Ph-6,8,9-PC(2)B(7)H(9)(2)(-) (1a(2)()(-)()) readily formed eta(4)-coordinated complexes with late transition metals including 8-Ph-7-(Ph(3)P)(2)-nido-7,8,10,11-PtPC(2)B(7)H(9) (9), 7-Ph-11-(eta(5)-C(5)H(5))-nido-11,7,9,10-CoPC(2)B(7)H(9) (10), and commo-Ni-(7-Ni-8'-Ph-nido-8',10',11'-PC(2)B(7)H(9))(7-Ni-8-Ph-nido-8,10,11-PC(2)B(7)H(9)) (11).     

Encapsulation of hydride by molecular main group metal clusters: manipulating the source and coordination sphere of the interstitial ion

The sequential treatment of Lewis acids with N,N'-bidentate ligands and thereafter with ButLi has afforded a series of hydride-encapsulating alkali metal polyhedra. While the use of Me3Al in conjunction with Ph(2-C5H4N)NH gives Ph(2-C5H4N)NAlMe2 and this reacts with MeLi in thf to yield the simple 'ate complex Ph(2-C5H4N)NAlMe3Li.thf, the employment of an organolithium substrate capable of beta-hydride elimination redirects the reaction significantly. Whereas the use of ButLi has previously yielded a main group interstitial hydride in which H- exhibits micro6-coordination, it is shown here that variability in the coordination sphere of the encapsulated hydride may be induced by manipulation of the organic ligand. Reaction of (c-C6H11)(2-C5H4N)NH with Me3Al/ButLi yields [{(c-C6H11)(2-C5H4N)N}6HLi8]+[(But2AlMe2)2Li]-, which is best viewed as incorporating only linear di-coordination of the hydride ion. The guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) in conjunction with Me2Zn/ButLi yields the micro8-hydride [(hpp)6HLi8]+[But3Zn]-.0.5PhMe. Formation of the micro8-hydride [(hpp)6HLi8]+[ButBEt3]- is revealed by employment of the system Et3B/ButLi. A new and potentially versatile route to interstitial hydrides of this class is revealed by synthesis of the mixed borohydride-lithium hydride species [(hpp)6HLi8]+[Et3BH]- and [(hpp)6HLi8]+[(Et3B)2H]- through the direct combination of hppLi with Et3BHLi.     

Cationic Rh complexes with novel spiro tetraarylpentaborate anions prepared from arylboronic acids and aryloxorhodium complexes

Ar-B(OH)2 (1a: Ar = C6H4OMe-4, 1b: Ar = C6H3Me2-2,6) react immediately with Rh(OC6H4Me-4)(PMe3)3 (2) in 5 : 1 molar ratio at room temperature to generate [Rh(PMe3)4]+[B5O6Ar4]- (3a: Ar = C6H4OMe-4, 3b: Ar = C6H3Me2-2,6). p-Cresol (92%/Rh), anisole (80%/Rh) and H2O (364%/Rh) are formed from 1a and 2. The reaction of 1a with 2 for 24 h produces [Rh(PMe3)4]+[B5O6(OH)4]- (4) as a yellow solid. This is attributed to hydrolytic dearylation of once formed 3a because the direct reaction of 3a with excess H2O forms 4. An equimolar reaction of 2 with phenylboroxine (PhBO)3 causes transfer of the 4-methylphenoxo ligand from rhodium to boron to produce [Rh(PMe3)4]+[B3O3Ph3(OC6H4Me-4)]- (5). Arylboronic acids 1a and 1b react with Rh(OC6H4Me-4)(PR3)3 (6: R = Et, 8: R = Ph) and with Rh(OC6H4Me-4)(cod)(PR3) (11: R = iPr, 12: R = Ph) to form [Rh(PR3)4]+[B5O6Ar4]- (7a: R = Et, Ar = C6H4OMe-4, 7b: R = Et, Ar = C6H3Me2-2,6, 9a: R = Ph, Ar = C6H3Me2-2,6) and [Rh(cod)(PR3)(L)]+[B5O6Ar4]- (13b: R = iPr, L = acetone, Ar = C6H3Me2-2,6, 14a: R = Ph, L = PPh3, Ar = C6H4OMe-4, 14b: R = Ph, L = PPh3, Ar = C6H3Me2-2,6), respectively. Hydrolysis of 14a yields [Rh(cod)(PPh3)2]+[B5O6(OH)4]- (15) quantitatively.     

Cationic diiron and diruthenium μ-allenyl complexes: synthesis, X-ray structures and cyclization reactions with ethyldiazoacetate/amine affording unprecedented butenolide- and furaniminium-substituted bridging carbene ligands

The novel cationic diiron μ-allenyl complexes [Fe(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 4a; R = Ph, 4b) have been obtained in good yields by a two-step reaction starting from [Fe(2)Cp(2)(CO)(4)]. The solid state structures of [4a][CF(3)SO(3)] and of the diruthenium analogues [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}][BPh(4)] (R = Me, [2a][BPh(4)]; R = Ph, [2c][BPh(4)]) have been ascertained by X-ray diffraction studies. The reactions of 2c and 4a with Br?nsted bases result in formation of the μ-allenylidene compound [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(1)-C(α)=C(β)=C(γ)(Ph)(2)}] (5) and of the dimetallacyclopentenone [Fe(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)=C(β)(C(γ)(Me)CH(2))C(=O)}] (6), respectively. The nitrile adducts [Ru(2)Cp(2)(CO)(NCMe)(μ-CO){μ-η(1):η(2)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 7a; R = Ph, 7b), prepared by treatment of 2a,c with MeCN/Me(3)NO, react with N(2)CHCO(2)Et/NEt(3) at room temperature, affording the butenolide-substituted carbene complexes [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(R)(2)OC(=O)C[upper bond 1 end](H)] (R = Me, 10a; R = Ph, 10b). The intermediate cationic compound [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (9) has been detected in the course of the reaction leading to 10a. The addition of N(2)CHCO(2)Et/NHEt(2) to 7a gives the 2-furaniminium-carbene [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (11). The X-ray structures of 10a, 10b and [11][BF(4)] have been determined. The reactions of 4a,b with MeCN/Me(3)NO result in prevalent decomposition to mononuclear iron species.     

Interaction of tertiary phosphines with lignin-type, alpha,beta-unsaturated aldehydes in water

To learn more about the bleaching action of pulps by (hydroxymethyl)phosphines, lignin chromophores, such as the alpha,beta-unsaturated aromatic aldehydes, sinapaldehyde, coniferylaldehyde, and coumaraldehyde, were reacted with the tertiary phosphines R2R'P [R = R' = Me, Et, (CH2)3OH, iPr, cyclo-C6H11, (CH2)2CN; R = Me or Et, R' = Ph; R = Ph, R' = Me, m-NaSO3-C6H4] in water at room temperature under argon. In all cases, initial nucleophilic attack of the phosphine occurs at the activated C=C bond to form a zwitterionic monophosphonium species. With the phosphines PR3 [R = Me, Et, (CH2)3OH] and with R2R'P (R = Me or Et, R' = Ph), the zwitterion undergoes self-condensation to give a bisphosphonium zwitterion that can react with aqueous HCl to form the corresponding dichloride salts (as a mixture of R,R- and S,S-enantiomers); X-ray structures are presented for the bisphosphonium chlorides synthesized from the Et3P and Me3P reactions with sinapaldehyde. With the more bulky phosphines, iPr3P, MePPh2, (cyclo-C6H11)3P, and Na[Ph2P(m-SO3-C6H4)], only an equilibrium of the monophosphonium zwitterion with the reactant aldehyde is observed. The weakly nucleophilic [NC(CH2)2]3P does not react with sinapaldehyde. An analysis of some exceptional 1H NMR data within the prochiral phosphorus centers of the bisphosphonium chlorides is also presented.     

Reactions of amides with organoaluminum compounds: factors affecting the coordination mode of aluminum amidates

Factors affecting the coordination mode of an amidato group on aluminum will be presented. The reaction of N-tert-butylalkylacetamide ((t)BuNHCR([double bond]O)) with 1.1 molar equiv of Me(3)Al in refluxing hexane affords a pentacoordinated, dimeric compound [Me(2)Al[eta(2)-(t)BuNC(R)(mu(2)-O)]](2) (3, R = p-(t)Bu-C(6)H(4); 4, R = 2,6-F,F-C(6)H(3); 5, R = Me; 6, R = CF(3); 7, R = p-F(3)C-C(6)H(4)). However, in the presence of 2.2 molar equiv of Me(3)Al, N-tert-butyl-4-tert-butylbenzamide ((t)BuNHC(p-(t)Bu-C(6)H(4))([double bond]O in refluxing hexane gives [Me(2)Al[eta(2)-(t)BuNC(p-(t)Bu-C(6)H(4))(mu(2)-O)]AlMe(3)], 8. In contrast, the reaction of R'NHCR' '([double bond]O) with 1 molar equiv of R(3)Al at room temperature produces tetracoordinated, dimeric, eight-membered ring aluminum compounds [R(2)Al[mu,eta(2)-R'NC(R' ')O]](2) (9, R = Me, R' = 2,6-(i)Pr, (i)()Pr-C(6)H(3), R' ' = Ph; 10, R = Me, R' = (i)Bu, R' ' = Ph; 11, R = Et, R' = Bn, R' ' = Ph; 12, R = Me, R' = Ph, R' ' = CF(3); 13, R = Me, R' = Bn, R' ' = CF(3)). On the other hand, 4'-chlorobenzanilide ((p-Cl-C(6)H(4))NHCPh([double bond]O)) reacts with R(3)Al to produce trimeric, twelve-membered ring aluminum compounds [R(2)Al[mu, eta(2)-(p-Cl-C(6)H(4))NC(Ph)O]](3) (14, R = Me; 15, R = Et). Furthermore, the reaction of 2'-methoxybenzanilide with 1 molar equiv of Me(3)Al in hexane yields a dinuclear aluminum complex [Me(2)Al(o-OMe-Ph)NC(Ph)(O)AlMe(3)], 16.     

Monocarbaborane chemistry. Preparation and characterisation of [4-CB8H9]-, the 'missing' closo-carbaborane anion

Thermolysis in the solid state of Cs+[arachno-CB9H14]-, or of Cs+[nido-CB9H12]-, or the oxidation of nido-1-CB8H12 with I2 in THF at -78 degrees C in the presence of NEt3, gives the first nine-vertex closo monocarbaborane, the stable [closo-4-CB8H9]- anion, in yields of 56, 61 and 75%, respectively.     

Diphosphacarbollide analogues of the C5H5- anion: isolation of the nido-di- and triphosphacarboranes 7,8,9-P2CB8H10, [7,8,9-P2CB8H9]-, [7,8,10-P2CB8H9]-, and 7,8,9,10-P3CB7H8

Treatment of a solution of excess PCl(3) and PS (PS = "proton sponge" = 1,8-dimethylamino naphthalene) with arachno-4-CB(8)H(14) (1) in CH(2)Cl(2), followed by hydrolysis of the reaction mixture, resulted in the isolation of the eleven-vertex diphosphacarbaborane nido-7,8,9-P(2)CB(8)H(10) (2) (yield 34%) as the main product. Other products isolated from this reaction were the phosphacarboranes nido-7,8,9,10-P(3)CB(7)H(8) (3) (yield 5%) and closo-2,1-PCB(8)H(9) (4) (yield 15%). Compound 2 can be deprotonated by PS in CH(2)Cl(2) or NaH in diethyl ether to give the [nido-7,8,9-P(2)CB(8)H(9)](-) (2(-)()) anion, which gives back the original compound, 2, upon re-protonation. Thermal rearrangement of anion 2(-) (Na(+) salt) at 350 degrees C for 2 h produced the isomeric [nido-7,8,10-P(2)CB(8)H(9)](-) (5(-)()) anion, which was isolated as a PPh(4)(+) salt (yield 86%). Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B] COSY, (1)H{(11)B(selective)}, (1)H{(31)P(selective)}, and gradient-enhanced ([(1)H-(13)C] HSQC) magnetic resonance measurements led to complete assignments of all resonances which are in excellent agreement with the structures proposed. Coupling constants, (1)J((31)P,(13)C), (2)J((31)P,C,(1)H), and (1)J((31)P,(31)P), were calculated using the DFT method B3LYP/6-311+G(d,p). The molecular geometries of all compounds were optimized ab initio at a correlated level of theory (RMP2(fc)) using the 6-31G basis set, and their correctness was assessed by comparison of the experimental (11)B and (13)C chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G method. The computations also include the structures and chemical shieldings of the still unknown isomers [nido-7,10,8-P(2)CB(8)H(9)](-) (6(-)) and [nido-7,9,8-P(2)CB(8)H(9)](-) (7(-)).     

Molecular structures of arachno-decaborane derivatives 6,9-X2B8H10 (X = CH2, NH, Se) including a gas-phase electron-diffraction study of 6,9-C2B8H14

The molecular structures of the three heterodecaboranes arachno-6,9-C2B8H14, arachno-6,9-N2B8H12, and arachno-6,9-Se2B8H10 have been determined by ab initio MO theory. In addition, the structure of arachno-6,9-C2B8H14 was experimentally determined using gas-phase electron diffraction (GED). The accuracy of all four of these structures has been confirmed by the good agreement of the (11)B chemical shifts calculated at the GIAO-MP2 level with the experimental values. A comparison of the GIAO-HF and GIAO-MP2 methods shows that for these heteroborane clusters, electron correlation effects on the computed delta((11)B) values are quite substantial and that it is necessary to go beyond the HF level in the NMR computation.     

Synthons for coordinatively unsaturated complexes of tungsten, and their use for the synthesis of high oxidation-state silylene complexes

Reduction of Cp*WCl4 afforded the metalated complex (eta6-C5Me4CH2)(dmpe)W(H)Cl (1) (Cp* = C5Me5, dmpe = 1,2-bis(dimethylphosphino)ethane). Reactions with CO and H(2) suggested that 1 is in equilibrium with the 16-electron species [Cp(dmpe)WCl], and 1 was also shown to react with silanes R2SiH2 (R2 = Ph2 and PhMe) to give the tungsten(IV) silyl complexes Cp*(dmpe)(H)(Cl)W(SiHR2) (6a, R2 = Ph2; 6b, R2 = PhMe). Abstraction of the chloride ligand in 1 with LiB(C6F5)4 gave a reactive species that features a doubly metalated Cp ligand, [(eta7-C5Me3(CH2)2)(dmpe)W(H)2][B(C6F5)4] (4). In its reaction with dinitrogen, 4 behaves as a synthon for the 14-electron fragment [Cp*(dmpe)W]+, to give the dinuclear dinitrogen complex ([Cp*(dmpe)W]2(micro-N2)) [B(C6F5)4]2 (5). Hydrosilanes R2SiH2 (R2 = Ph2, PhMe, Me2, Dipp(H); Dipp = 2,6-diisopropylphenyl) were shown to react with 4 in double Si-H bond activation reactions to give the silylene complexes [Cp*(dmpe)H2W = SiR2][B(C6F5)4] (8a-d). Compounds 8a,b (R2 = Ph2 and PhMe, respectively) were also synthesized by abstraction of the chloride ligands from silyl complexes 6a,b. Dimethylsilylene complex 8c was found to react with chloroalkanes RCl (R = Me, Et) to liberate trialkylchlorosilanes RMe2SiCl. This reaction is discussed in the context of its relevance to the mechanism of the direct synthesis for the industrial production of alkylchlorosilanes.     

Monocarbaborane anion chemistry. The elusive C-arylated [PhCB11H11]-, [PhCB9H9]- and [PhCB8H8]- anions

B10H14 and PhCHO yield [6-Ph-nido-6-CB9H11]- (94%), from which the nine-vertex C-phenyl monocarbaborane anion [4-Ph-closo-4-CB8H8]- (68%) can be obtained by heating at 200 degrees C, and from which the twelve- and ten-vertex analogues [1-Ph-closo-1-CB11H11]- (50%) and [4-Ph-closo-4-CB9H9]- (25%) can be obtained by heating at 210 degrees C with BH3(NEt3).