Sihai Li

Allyl(carborane) complexes of the group 6 metals : protonation studies with aqueous HI

Abstract Treatment of CH 2 Cl 2 solutions of [N(PPh 3 ) 2 ][ closo -1,2-Me 2 -3-(η 3 -C 3 H 5 )-3,3-(CO) 2 -3,1,2-WC 2 B 9 H 9 ] with aqueous HI in the presence of CO affords [N(PPh 3 ) 2 ][ closo -1,8-Me 2 -2-I-2,2,2-(CO) 3 -2,1,8-WC 2 B 9 H 9 ] in virtually quantitative yield. In contrast, the reaction between [N(PPh) 3 ) 2 ][ closo -1,2-Me 2 -3-(η 3 -C 3 H 5 )-3,3-(CO) 2 -3,1,2-MoC 2 B 9 H 9 ] and aqueous HI gives initially [N(PPh 3 ) 2 ][ closo -1,2-Me 2 -3-I-3,3,3-(CO) 3 -3,1,2-MoC 2 B 9 H 9 ], but the latter undergoes a cage framework rearrangement to afford [N(PPh 3 ) 2 ][ closo -1,8-Me 2 -2-I-2,2,2-(CO) 3 -2,1,8-MoC 2 B 9 H 9 , which is slow at room temperature. Protonation of [NEt 4 ][ closo -1,2-Me 2 -3-(CC 6 H 4 Me-4)-3,3-(CO) 2 -3,1,2-MoC 2 B 9 H 9 ] with aqueous HI yields initially [NEt 4 ][ closo -1,2,-Me 2 -8-(CH 2 C 6 H 4 Me-4)-3-I-3,3,3-(CO) 3 -3,1,2-MoC 2 B 9 H 8 ], which isomerizes at room temperature to give [NEt 4 ][ closo -1,8-Me 2 -11-(CH 2 C 6 H 4 Me-4)-2-I-2,2,2-(CO) 3 -2,1,8-MoC 2 B 9 H 8 ]. The reaction between [N(PPh 3 )2][ closo -1,8-Me 2 -2,I-2,2,2-(CO) 3 -2,1,8-MoC 2 B 9 H 9 ] and [W(CC 6 H 4 Me-4)(CO) 2 (η-C 5 H 5 )] in CH 2 Cl 2 in the presence of TIPF 6 affords mainly [MoW(μ-CC 6 H 4 Me-4)(CO) 3 (η 5 - nido -2,8-Me 2 -2,8-C 2 B 9 H 9 )(η-C 5 H 5 )] together with some of its polytopal isomer [MoW(μ-CC 6 H 4 Me-4)(CO) 3 (η 5 - nido -7,8-Me 2 -7,8-C 2 B 9 H 9 )(η-C 5 H 5 )].

Synthesis of the complexes [N(PPH3)2][M(CO)2(η3-C3H5)-(η6-7, 9-C2B10H10Me2)](M = Mo or W): crystal structure of [N(PPH3)2][WBr(CO) 3(η6-7,9-C2B10H10Me2)]

Abstract Treatment of the compounds [MBr(CO)2(NCMe)2(η3-C3H5)] (M = Mo or W) with Na2[7,9-C2B10H10Me2] in tetrahydrofuran, followed by addition of [N(PPh3) 2]Cl, affords the salts [N(PPh3)2][M(CO)2(η3-C3H5)(η6-7,9-C2 B10H10Me2)]. Reactions of [N(PPh3)2]2[M(CO)3(η6-7,9-C2B10H 10Me2)] with an excess of allyl bromide generate the complexes [N(PPh3)2][MBr(CO)3 (η6-7,9-C2B10H10Me2)] via an allyl-coupling process. The structure of the latter (M = W) has been determined by X-ray diffraction. The preparation of the molybdenum salt [N(PPh3)2] [MoBr(CO)3(η6-7,9-C2B10H10Me2)] by this route was accompanied by the formation of small amounts of the complex [N(PPh3)2][MoBr(CO)3(η5-7,9-C2B9H9Me2)] resulting from ejection of a BH vertex from the cage. Indeed, it was observed that in CH2Cl2 solutions, the former species was slowly converted into the latter at ambient temperatures. Protonation (aqueous HBr) of the salts [N(PPh3)2][M(CO)2(η3-C3H5)(η6-7,9-C2B10H10Me2)] in the presence of an atmosphere of CO also yields the compounds [N(PPh3)2][MBr(CO)3(η6-7,9-C 2B10H10Me2)], but if the molybdenum compound is protonated in the absence of CO the complex [N(PPh3)2][MoBr(CO)3(η5-7,9-C2B9H9Me2)] is formed directly. The NMR data for the new compounds are reported and discussed, as are the possible pathways of their formation.

Alkyne–carbaborane coupling at a molybdenum centre: crystal structure of [closo-3,3,3-(CO)3-8,3-{σ:η2-C(H)C(H)-SiMe3}-3,1,2-MoC2B9H10]

In CH2Cl2 the complex [closo-1,2-Me2-3-(η-PhC2Ph)-3-(CO)-3-(PPh3)-3,1,2-MoC2B9H9] decomposed to yield a mixture of [closo-1,2-Me2-3,3,3-(CO)3-3-(PPh3)-3,1,2-MoC2B9H9] and [closo-1,2-Me2-3,3-(CO)2-3-(PPh3)-8,3-{σ:η2-C(Ph)C(H)Ph}-3,1,2-MoC2B9H8]. Protonation (HBF4·Et2O) of [NEt4][closo-3-(η-C3H5)-3,3-(CO)2-3,1,2-MoC2B9H11], in CH2Cl2 at – 78 °C, in the presence of an excess of Me3SiCCSiMe3, afforded a chromatographically separable mixture of [closo-3,3-(η-Me3SiC2SiMe3)2-3-(CO)-3,1,2-MoC2B9H11] and [closo-3,3,3-(CO)3-8,3-{σ:η2-C(H)C(H)SiMe3}-3,1,2-MoC2B9H10]. The latter complex forms via the intermediacy of Me3SiCCH, generated by HF cleavage of Me3SiCCSiMe3, and its structure was established by X-ray diffraction. The molybdenum atom is ligated on one side by three CO groups, and on the other by the open pentagonal face of the nido-1,2-C2B9 cage framework. The boron atom located in the β site with respect to the two carbons carries a vinyl substitutent C(H)C(H)SiMe3, and this exopolyhedral group is η2 co-ordinated to the molybdenum atom [Mo-C 2.43(1) and 2.55(1)A]. Treatment of [N(PPh3)2][closo-1,2-Me23-(η-C3H5)-3,3-(CO)2-3,1,2-MoC2B9H9] and Me3SiCCH with HBF4·Et2O gives initially the complex [closo-1,2-Me2-3,3-(η-Me3SiC2H)2-3-(CO)-3,1,2-MoC2B9H9], which subsequently rearranges to [closo-1,2-Me2-3-(η-Me3SiC2H)-3-(CO)-8,3-{σ:η2-C(H)C(H)SiMe3}-3,1,2-MoC2B9H8]. Use of Me3SiCCD in this synthesis, combined with NMR studies, suggests that insertion of the alkyne into the cage B–H bond proceeds via the intermediacy of a molybdenum vinylidene species. The NMR data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) for the new compounds are reported and discussed in relation to the structures proposed.

An allyl(carborane)nitrosyl molybdenum complex : preparation and reactivity

Abstract Treatment of CH2Cl2 solutions of [NEt4][closo-3-(η3-C3H5)-3,3-(CO)2-3,1,2-MoC2B9H11] with [NO][BF4] at room temperature affords the allyl(carborane)nitrosyl complex [closo-3-(η3-C3H5)-3-(CO)-3-(NO)-3,1,2-MoC2B9H11] in moderate yield. Reaction between the latter compound and K-Selectride (K[BH(Bus)3]) in thf, followed by the addition of [N(PPh3)2]Cl affords the η2-alkene complex [N(PPh3)2][closo-3-(η2-CH2CHEMe)-3-(CO)-3-(NO)-3,1,2-MoC2B9H11]. Similarly, the complex [N(PPh3)2][closo-3-(η2-CH2CHEt)-3-(CO)-3-(NO)-3,1,2-MoC2B9H11] is obtained from the reaction between [closo-3-(η3-C3H5)-3-(CO)-3-(NO)-3,1,2-MoC2B9H11] and methyl lithium, followed by the addition of [N(PPh3)2]Cl. Treating CH2Cl2 solutions of the allyl-nitrosyl complex with the nucleophiles PPh3 and Ph3PCHC(O)Me affords the complexes [closo-3-(η2-CH2CHCH2PPh3)-3-(CO)-3-(NO)-3,1,2-MoC2B9H11] and [closo-3-{η2-CH2CH CH2CH(PPh3)C(O)Me}-3-(CO)-3-(NO)-3,1,2-MoC2B9H11], respectively. The IR and NMR data (1H, 11B{1H}, 13C{1H} and 31P{1H}) for the new complexes are reported and discussed in relation to their structures.

Protonation of the alkylidynetungsten complexes [W(CR)(CO)2(η-C5H5)](R = C6H4Me-2, C6H3Me2-2,6 or C6H4OMe-2)

The complexes [W(CR)(CO)2(η-C5H5)](R = C6H4Me-2 or C6H3Me2-2,6) react with 2 equivalents of CF3CO2H in CH2Cl2 to afford [W(O2CCF3)2(CO)(η2-COCH2R)(η-C5H5)], and with 2 equivalents of HBF4·Et2O in NCMe to give the salts [W(CO)(NCMe)2(η2-COCH2R)(η-C5H5)][BF4]2. Treatment of [W(CC6H4OMe-2)(CO)2(η-C5H5)] with ca. 0.5 equivalent of HBF4·Et2O in CH2Cl2 at ca. –78 °C gives the salt [W{C(H)C6H4OMe-2}(CO)2(η-C5H5)][BF4]. However, if the reaction of [W(CC6H4OMe-2)(CO)2(η-C5H5)] with 1 equivalent of HBF4·Et2O is carried out in the presence of PPh3 or Ph2PCH2PPh2 the complexes [W{σ,η2-CH(PPh3)C6H4OMe-2}(CO)2(η-C5H5)][BF4] and [[graphic omitted]Ph2}(CO)2(η-C5H5)][BF4], respectively, are obtained. The structure of the former has been established by X-ray diffraction. In the cation the tungsten atom is ligated by the cyclopentadienyl group, two CO molecules (W–C–O average 176°), and by a CH(PPh3)C6H4OMe-2 fragment. The latter is attached to the metal in a σ,η2-bonding mode via a W–CH(PPh3) linkage [2.16(3)A] and connectivities to two carbon atoms of the C6H4OMe-2 ring [W–C1 2.31(3) and W–C6 2.65(4)A].

Alkylidyne(carbaborane) complexes of the Group 6 metals. Part 5. Protonation studies on [NEt4][W(CC6H4OMe-2)(CO)2(η5-C2B9H9Me2)]

Dichloromethane solutions of [NEt4][W(CR)(CO)2(η5-C2B9H9Me2)](R = C6H4OMe-2) at –78 °C on treatment with HBF4·Et2O in the presence of the substrates L = CO, PPh3, PHPh2, CNBut and PhC2Ph afford the complexes [W(CO)2L2{η5-C2B9H8(CH2R)Me2}](L = CO, PHPh2 or CNBut), [W(CO)3(PPh3){η5-C2B9H8(CH2R)Me2}] and [W(CO)(PhC2Ph)2{η5-C2B9H8(CH2R)Me2}] respectively. The corresponding protonation reaction employing dppm (Ph2PCH2PPh2) as the substrate yields [W(CO)2(dppm){η5-C2B9H8(CH2R)Me2}] as the major product, together with small quantities of [[graphic omitted]Ph2}(CO)2(η5-C2B9H9Me2)]. The structure of [W(CO)3(PPh3){η5-C2B9H8-(CH2R)Me2}] has been established by X-ray diffraction. The tungsten atom is η5 co-ordinated by the nido-icosahedral fragment C2B9H8(CH2R)Me2. In the latter the exopolyhedral CH2R group is bonded to the boron atom which is in the β position with respect to the two carbon atoms in the open pentagonal [graphic omitted] face of the cage ligating the tungsten. The latter also carries three terminally bound CO groups and the PPh3 ligand. Addition of aqueous HI to CH2Cl2 solutions of [NEt4][W(CR)(CO)2(η5-C2B9H9Me2)] affords the salt [NEt4][WI(CO)3{η5-C2B9H8(CH2R)Me2}]. In the latter there is a 2,1,8 arrangement for the non-boron vertices of the WC2B9 icosahedron, in contrast with the closo-3,1,2-WC2B9 structures of the other products. The NMR data (1H, 13C-{1H}, 11B-{1H} and 31P-{1H}) for the new compounds are reported and discussed in relation to the molecular structures.

Protonation of the alkylidynetungsten complex [W(CC6H4CH2OMe-2)(CO)2(η-C5H5)]

The complex [W(CC6H4CH2OMe-2)(CO)2(η-C5H5)] has been prepared and its protonation with HBF4·Et2O and aqueous HI investigated. In CH2Cl2 at –78 °C mixtures of the alkylidynetungsten compound and PPh3 on treatment with HBF4·Et2O afford the complex [W(CO)2{η4-C6H4(CH2)[CH(PPh3)]-1,2}(η-C5H5)][BF4]2, the structure of which has been established by X-ray crystallography. The C6H4(CH2)[CH(PPh3)]-1,2 ligand is η4-co-ordinated to the tungsten via the carbon atoms of the ortho CH and CH2 substituents of the C6H4 group and their respective ring carbons [W–C 2.30(2) to 2.41 (2)A]. The terminal CH fragment carries a PPh3 group P–C [1.81 (2)A]. The tungesten atom is also ligated by the C5H5 ring and two CO groups in the usual manner. Treatment of [W(CC6H4CH2OMe-2)(CO)2(η-C5H5)] with aqueous HI affords sequentially the alkylidene complex [W{C(H)C6H4CH2OMe-2}I(CO)2(η-C5H5)] and the acyl compound [WI2(CO)(η2-COCH2C6H4CH2OMe-2)(η-C5H5)]. Possible pathways to the new compounds are discussed, and their 1H and 13C-{1H} NMR spectra are reported.

Allyl(carbaborane) complexes of Group 6 metals: preparation and reactivity

Treatment of thf (tetrahydrofuran) solutions of [MBr(CO)2(NCMe)2(η3-C3H5)](M = Mo or W) with Na2[7,8-C2B9H9R′2](R′= H or Me), followed by addition of [N(PPh3)2]Cl or [NEt4]Cl, afforded the salts [Y][M(CO)2(η3-C3H5)(η5-7,8-C2B9H9R′2)][Y = N(PPh3)2, R′= Me, M = Mo 1a or W 1b; Y = NEt4. R′= H, M = Mo 1c] in high yield. These species may be synthesised, but in lower yield, from allyl bromide and Tl2[M(CO)3(η5-7,8-C2B9H9R′2)] generated in situ. Protonation of the salts 1a and 1b with HBF4·Et2O in the presence of CO or PPh3 yielded the compounds [M(CO)2L2(η5-7,8-C2B9H9Me2)](M = Mo 2a or W 2b, L = CO; M = Mo 2c or W 2e, L = PPh3). The synthesis of 2c was accompanied by formation of the tricarbonyl species [Mo(CO)3(PPh3)(η5-7,8-C2B9H9Me2)]2d. Treatment of the salt 1c with HBF4·Et2O in the presence of buta-1,3-diene afforded the species [Mo(CO)2(η4-C4H6)(η5-7,8-C2B9H11)]5. When reactions of 1a–c with HBF4·Et2O were carried out in the presence of alkynes, the bis(alkyne) complexes [M(CO)(RC2R)2(η5-7,8-C2B9H9R′2)](M = Mo, R = R′= Me 6a; M = W, R = Ph, R′= Me 6b; M = Mo, R = Me, R′= H 6c) are formed. The compounds 6a and 6c can also be obtained from reactions between Tl2[Mo(CO)3(η5-7,8-C2B9H9R′2)] generated in situ, MeC≡CMe, and AgBF4. Reaction of the complex 6a with PMe2Ph gives the species [Mo(CO)(PMe2Ph)(MeC2Me)(η5-7,8-C2B9H9Me2)]6e. Treatment of the reagent Tl2[Mo(CO)3(η5-7,8-C2B9H9Me2)] with AgBF4 in the presence of [W(≡CC6H4-Me-4)(CO)2(η-C5H5)] afforded the dimetal complex [MoW(µ-CC6H4Me-4)(CO)3(η-C5H5)(η5-7,8-C2B9H9Me2)]7.