Bifunctional rhenium complexes for the catalytic transfer-hydrogenation reactions of ketones and imines

The silyloxycyclopentadienyl hydride complexes [Re(H)(NO)(PR(3))(C(5)H(4)OSiMe(2)tBu)] (R=iPr (3 a), Cy (3 b)) were obtained by the reaction of [Re(H)(Br)(NO)(PR(3))(2)] (R=iPr, Cy) with Li[C(5)H(4)OSiMe(2)tBu]. The ligand-metal bifunctional rhenium catalysts [Re(H)(NO)(PR(3))(C(5)H(4)OH)] (R=iPr (5 a), Cy (5 b)) were prepared from compounds 3 a and 3 b by silyl deprotection with TBAF and subsequent acidification of the intermediate salts [Re(H)(NO)(PR(3))(C(5)H(4)O)][NBu(4)] (R=iPr (4 a), Cy (4 b)) with NH(4)Br. In nonpolar solvents, compounds 5 a and 5 b formed an equilibrium with the isomerized trans-dihydride cyclopentadienone species [Re(H)(2)(NO)(PR(3))(C(5)H(4)O)] (6 a,b). Deuterium-labeling studies of compounds 5 a and 5 b with D(2) and D(2)O showed H/D exchange at the H(Re) and H(O) positions. Compounds 5 a and 5 b were active catalysts in the transfer hydrogenation reactions of ketones and imines with 2-propanol as both the solvent and H(2) source. The mechanism of the transfer hydrogenation and isomerization reactions was supported by DFT calculations, which suggested a secondary-coordination-sphere mechanism for the transfer hydrogenation of ketones.     

H(2) activation and hydride transfer to olefins by al(c(6) f(5) )(3) -based frustrated lewis pairs

Frustrated delivery: Frustrated Lewis pairs derived from tBu(3) P and Al(C(6) F(5) )(3) activate H(2) to give [tBu(3) PH][(μ-H)(Al(C(6) F(5) )(3) )(2) ], which reacts with unactivated olefins to give RAl(C(6) F(5) )(2) (R=Et or Cy) and [tBu(3) PH][Al(C(6) F(5) )(4) ]. The proposed mechanism involves olefin activation by aluminum, which is supported by the isolation of the cyclohexene complex [Al(C(6) F(5) )(3) ?(C(6) H(10) )].     

Synthesis and reactivity of the phosphinoboranes R2PB(C6F5)2

The phosphinoboranes [R(2)PB(C(6)F(5))(2)](2) (R = Et 1, Ph 2) and R(2)PB(C(6)F(5))(2) (R = tBu 3, Cy 4, Mes 5) were synthesized from the reaction of (C(6)F(5))(2)BCl and the corresponding lithium phosphide. The relationships between B-P distance, P pyramidality, and the extent of BP multiple bonding were further explored computationally. Natural Bond Order (NBO) analyses of 3 and 4 showed that the π-bonding highest occupied molecular orbitals (HOMOs) were highly polarized. In addition the Lewis acid-base adducts, R(2)(H)P·B(H)(C(6)F(5))(2) (R = Et 6; Ph 7; tBu 8; Cy 9; Mes 10) were prepared via the reaction of the phosphines R(2)PH with the borane HB(C(6)F(5))(2). Compounds 1 and 2 showed no signs of reaction with H(2); however, reaction of compounds 3 and 4 with H(2) was observed to give 8 and 9. In a related set of reactions compounds 3 and 4 were reacted with H(3)NBH(3) or Me(2)(H)NBH(3) also led to the generation of 8 and 9, respectively. The reaction profile of the reaction of (CF(3))(2)BPR(2) with H(2) was examined computationally and shown to be exothermic. Efforts to effect the reverse reaction, that is, dehydrogenation of adducts 6-10 were unsuccessful. Compound 4 was also shown to react with 4-tert-butylpyridine to give Cy(2)PB(C(6)F(5))(2)(4-tBuC(5)H(4)N) 11 while reactions of 3 and 4 with the Lewis acid BCl(3) gave the dimers (R(2)PBCl(2))(2) (R = tBu 12, Cy 13) and the byproduct ClB(C(6)F(5))(2).     

Reaction of Tungsten–Phosphinidene and –Arsinidene Complexes with Carbodiimides and Alkyl Azides: A Straightforward Way to Four‐Membered Heterocycles

The reaction of the phosphinidene and arsinidene complexes [Cp*E{W(CO)₅}₂] (E=P ( 1 a ), As ( 1 b ); Cp*=C₅Me₅) with carbodiimides leads to the new four‐membered heterocycles of the type [Cp*C(NR)₂E{W(CO)₅}₂] (E=P: R=iPr ( 2 a ), Cy ( 3 a ); E=As: R=iPr ( 2 b ), Cy ( 3 b )). The reaction of phosphinidene complex 1 a with alkyl azides yields the triazaphosphete derivatives [Cp*P{W(CO)₅}N(R)NN{W(CO)₅}] (R=Hex, Cy) ( 4 ). These unprecedented N₃P four‐membered triazaphosphete complexes can be regarded as stabilized intermediates of the Staudinger reaction, which have not been previously isolated. All of the isolated products were characterized by NMR, IR spectroscopy, mass spectrometry, and by single‐crystal X‐ray diffraction analysis.     

Ni, Pd, Pt, and Ru complexes of phosphine-borate ligands

The species Cy(2)PHC(6)F(4)BF(C(6)F(5))(2) reacts with Pt(PPh(3))(4) to yield the new product cis-(PPh(3))(2)PtH(Cy(2)PC(6)F(4)BF(C(6)F(5))(2)) 1 via oxidative addition of the P-H bond of the phosphonium borate to Pt(0). The corresponding reaction with Pd(PPh(3))(4) affords the Pd analogue of 1, namely, cis-(PPh(3))(2)PdH(Cy(2)PC(6)F(4)BF(C(6)F(5))(2)) 3; while modification of the phosphonium borate gave the salt [(PPh(3))(3)PtH][(tBu(2)PC(6)F(4)BF(C(6)F(5))(2))] 2. Alternatively initial deprotonation of the phosphonium borate gave [tBu(3)PH][Cy(2)PC(6)F(4)BF(C(6)F(5))(2)] 4, [SIMesH][Cy(2)PC(6)F(4)BF(C(6)F(5))(2)] 5 which reacted with NiCl(2)(DME) yielding [BaseH](2)[trans-Cl(2)Ni(Cy(2)PC(6)F(4)BF(C(6)F(5))(2))(2)] (Base = tBu(3)P 6, SIMes 7) or with PdCl(2)(PhCN)(2) to give [BaseH](2)[trans-Cl(2)Pd(Cy(2)PC(6)F(4)BF(C(6)F(5))(2))(2)] (Base = tBu(3)P 8, SIMes 9). While [C(10)H(6)N(2)(Me)(4)H][tBu(2)PC(6)F(4)BF(C(6)F(5))(2)] 10 was also prepared. A third strategy for formation of a metal complex of anionic phosphine-borate derivatives was demonstrated in the reaction of (COD)PtMe(2) with the neutral phosphine-borane Mes(2)PC(6)F(4)B(C(6)F(5))(2) affording (COD)PtMe(Mes(2)PC(6)F(4)BMe(C(6)F(5))(2)) 11. Extension of this reactivity to tBu(2)PH(CH(2))(4)OB(C(6)F(5))(3)) was demonstrated in the reaction with Pt(PPh(3))(4) which yielded cis-(PPh(3))(2)PtH(tBu(2)P(CH(2))(4)OB(C(6)F(5))(3)) 12, while the reaction of [SIMesH][tBu(2)P(CH(2))(4)OB(C(6)F(5))(3)] 13 with NiCl(2)(DME) and PdCl(2)(PhCN)(2) afforded the complexes [SIMesH](2)[trans-Cl(2)Ni(tBu(2)PC(4)H(8)OB(C(6)F(5))(3))(2)] 14 and [SIMesH](2)[trans-PdCl(2)(tBu(2)P(CH(2))(4)OB(C(6)F(5))(3))(2)] 15, respectively, analogous to those prepared with 4 and 5. Finally, the reaction of 7 and 13with [(p-cymene)RuCl(2)](2) proceeds to give the new orange products [SIMesH][(p-cymene)RuCl(2)(Cy(2)PC(6)F(4)BF(C(6)F(5))(2))] 16 and [SIMesH][(p-cymene)RuCl(2)(tBu(2)P(CH(2))(4)OB(C(6)F(5))(3))] 17, respectively. Crystal structures of 1, 6, 10, 11, 12, and 16 are reported.     

Catalytic P--H activation by Ti and Zr catalysts

Catalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts [Cp*2Zr(mu-H)3Li]3 (1 a) or [Cp*2Zr(mu-H)3K(thf)4] (1 b), and the metallocycles [CpTi(NPtBu3)(CH2)4] (6) and [Cp*M(NPtBu3)(CH2)4] (M=Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH2 (R=Ph, C6H2Me3, Cy, C10H7) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP)n (n=4, 5) while reaction of tBu3C6H2PH2 gave the phosphaindoline tBu2(Me2CCH2)C6H2PH 9. Stoichiometric reactions of these catalyst precursors with primary phosphines afforded [Cp*2Zr((PR)2)H][K(thf)4] (R=Ph 2, Cy 3, C6H2Me3 4), [Cp*2Zr((PPh)3)H][K(thf)4] (5), [CpTi(NPtBu3)(PPh)3] (7) and [CpTi(NPtBu3)(mu-PHPh)]2 (8), while reaction of 6 with (C6H2tBu3)PH2 in the presence of PMe3 afforded [CpTi(NPtBu3)(PMe3)(P(C6H2tBu3)] (10). The secondary phosphines Ph2PH and (PhHPCH2)2CH2 also undergo dehydrocoupling affording (Ph2P)2 and (PhPCH2)2CH2. The bisphosphines (CH2PH2)2 and C6H4(PH2)2 are dehydrocoupled to give (PCH2CH2PH)2)(12) and (C6H4P(PH))2 (13) while prolonged reaction of 13 gave (C6H4P2)(8) (14). The analogous bisphosphine Me2C6H4(PH)2 (17) was prepared and dehydrocoupling catalysis afforded (Me2C6H2P(PH))2 (18) and subsequently [(Me2C6H2P2)2(mu-Me2C6H2P2)]2 (19). Stoichiometric reactions with these bisphosphines gave [Cp*2Zr(H)(PH)2C6-H4][Li(thf)4] (22), [CpTi(NPtBu3)(PH)2C6H4]2 (23) and [Cp*Ti(NPtBu3)(PH)2C6H4] (24). Mechanistic implications are discussed.     

Synthesis and structure of boron-bridged constrained geometry complexes of titanium

The boron-bridged constrained geometry titanium complexes [Ti[eta5:eta1-(C5H4)B(NR2)NPh](NMe2)2][R = iPr (3), SiMe3(4)] and [Ti[eta5:eta1-(C9H6)B(NiPr2)NPh](NMe2)2](12) have been prepared in good yields by amine elimination reaction from [Ti(NMe2)4]. Subsequent deamination-chlorination with excess Me3SiCl yielded the corresponding dichloro-complexes (5, 6, 13). Reaction of the analogous ligand precursors (C5H5)B(NiPr2)N(H)R (R = Cy, tBu) with [Ti(NMe2)4] did not result in the expected bridged compounds, but rather in the half-sandwich complexes [Ti[(eta5-C5H4)B(NiPr2)N(H)R](NMe2)3][R = Cy (9), tBu (10)]. All compounds were fully characterised by means of multinuclear NMR spectroscopy. Thorough investigation of substituent effects was achieved by comparative X-ray diffraction studies on complexes 3, 5, 6 and 12.     

Ring openings of lactone and ring contractions of lactide by frustrated Lewis pairs

While B(C(6)F(5))(3) forms the adducts (CH(2))(4)CO(2)B(C(6)F(5))(3)1 and (CHMeCO(2))(2)B(C(6)F(5))(3)7 with δ-valerolactone and lactide, the frustrated Lewis pairs derived from B(C(6)F(5))(3) and phosphine or N-bases react with lactone to effect ring opening affording zwitterionic species of the form L(CH(2))(4)CO(2)B(C(6)F(5))(3) (L = tBu(3)P 2, Cy(3)P 3, C(5)H(3)Me(3)N 4, PhNMe(2) 5, C(5)H(6)Me(4)NH 6) while reaction with rac-lactide results in ring contraction to give salts [LH][OCCHMeCO(2)(CMe)OB(C(6)F(5))(3)] (L = tBu(3)P 8, Cy(3)P 9, C(5)H(3)Me(2)N 10, C(5)H(6)Me(4)NH 11). The mechanistic implications of these reactions are discussed.     

Tuning Lewis acidity using the reactivity of "frustrated Lewis pairs": facile formation of phosphine-boranes and cationic phosphonium-boranes

The concept of "frustrated Lewis pairs" involves donor and acceptor sites in which steric congestion precludes Lewis acid-base adduct formation. In the case of sterically demanding phosphines and boranes, this lack of self-quenching prompts nucleophilic attack at a carbon para to B followed by fluoride transfer affording zwitterionic phosphonium borates [R(3)P(C(6)F(4))BF(C(6)F(5))(2)] and [R(2)PH(C(6)F(4))BF(C(6)F(5))(2)]. These can be easily transformed into the cationic phosphonium-boranes [R(3)P(C(6)F(4))B(C(6)F(5))(2)](+) and [R(2)PH(C(6)F(4))B(C(6)F(5))(2)](+) or into the neutral phosphino-boranes R(2)P(C(6)F(4))B(C(6)F(5))(2). This new reactivity provides a modular route to a family of boranes in which the steric features about the Lewis acidic center remains constant and yet the variation in substitution provides a facile avenue for the tuning of the Lewis acidity. Employing the Gutmann-Beckett and Childs methods for determining Lewis acid strength, it is demonstrated that the cationic boranes are much more Lewis acidic than B(C(6)F(5))(3), while the acidity of the phosphine-boranes is diminished.     

Direct observation of reductive elimination of methyl iodide from a rhodium(III) pincer complex: the importance of sterics

A rare case of directly observed alkyl halide reductive elimination from rhodium is reported. Treatment of the naphthyl-based PCP-type Rh(III) methyl complexes 2a,b [(C10H5(CH2PR2)2)Rh(CH3)(I)] (R = iPr 2a, R = tBu 2b) with CO resulted in facile reductive elimination of methyl iodide in the case of 2b, yielding the Rh(I) carbonyl complex [(C10H5(CH2PR2)2)Rh(CO)] 3b (R = tBu), while the less bulky 2a formed CO adducts and did not undergo reductive elimination, contrary to expectations based on electron density considerations. Moreover, 3b oxidatively added methyl iodide, while 3a did not. CD3I/CH3I exchange studies in the absence of CO indicate that reversible formation of (ligated) methyl iodide takes place in both systems. Subsequently, when CO is present, it displaces methyl iodide in the bulkier tBu system, whereas with the iPr system formation of the Rh(III) CO adducts is favored. Iodide dissociation followed by its attack on the rhodium-methyl group is unlikely.     

Synthesis and structures of gold perfluorophthalimido complexes

Compounds of the new tetrafluorophthalimido anion, [C(6)F(4)(CO)(2)N](-), are readily accessible by treatment of tetrafluorophthalimide with either LiNPr(i)(2) or mixtures of NEt(3) and Me(3)ECl (E = Si or Sn), to give C(6)F(4)(CO)(2)N-X (X = Li 3, SiMe(3)4, and SnMe(3)5). The reaction of the trimethylsilyl derivative 4 with AgF leads cleanly to the ion pair complex [Ag(NCMe)(2)][Ag(N(CO)(2)C(6)F(4))(2)] (6·2MeCN), which contains a linear [Ag{N(CO)(2)C(6)F(4)}(2)](-) anion and a tetracoordinate Ag(+) cation. Compound 6 reacts with iodine to give the N-iodo compound C(6)F(4)(CO)(2)NI 7, which crystallises as an acetonitrile adduct. Treatment of 6 with LAuCl affords LAu{N(CO)(2)C(6)F(4)} (L = Ph(3)P 8a, Cy(3)P 8b, or THT 9), whereas the reaction with AuCl in acetonitrile affords the heterobinuclear compound [Ag(MeCN)(2)][Au{N(CO)(2)C(6)F(4)}(2)]·MeCN (10·3MeCN). The tetrafluorophthalimido ligand is not readily displaced by donor ligands; however, the addition of B(C(6)F(5))(3)(Et(2)O) to a diethyl ether solution of 8a leads to the salt [Au(PPh(3))(2)][N{COB(C(6)F(5))(3)}(2)C(6)F(4))] 11. The analogous reaction of (THT)Au{N(CO)(2)C(6)F(4)} with B(C(6)F(5))(3) in toluene in the presence of excess norbornene (nb) gives [Au(nb)(3)][N{COB(C(6)F(5))(3)}(2)C(6)F(4))] 12. Compounds 11 and 12 contain a new non-coordinating phthalimido-bridged diborate anion with O-bonded boron atoms. The crystal structures of compounds 2-11 are reported.     

Auration, argentation, and mercuration reactions of an iridaphosphirene

The reactions of the iridaphosphirene complex [Ir{=C(tBu)P(Cy)}(CO)(PPh3)2] (Cy = cyclohexyl) with either [AuCl(tht)] (tht = tetrahydrothiophene) or AgCl result in the products [Ir{=C(tBu)P[M(Cl)](Cy)}(CO)(PPh3)2], M = Au or Ag. The aurated product can additionally be obtained on reaction of the iridaphosphirene with [AuCl(CNtBu)], via loss of the isocyanide ligand. Treatment of [Ir{=C(tBu)P(Cy)}(CO)(PPh3)2] with [AuCl(PPh3)] in the presence of silver triflate leads to the isolation of the salt, [Ir{=C(tBu)P[Au(PPh3)](Cy)}(CO)(PPh3)2][SO3CF3]. Reaction of the iridaphosphirene with PhHgCl in the absence or presence of silver triflate affords the mercurated species [Ir{=C(tBu)P[Hg(Ph)](Cy)}(CO)(PPh3)2]X, X = Cl or CF3SO3, respectively. The former exhibits a weakly mercury-coordinated chloride ion. The X-ray crystal structures of all of the complexes are described.     

Synthesis and the thermal and catalytic dehydrogenation reactions of amine-thioboranes

A series of trimethylamine-thioborane adducts, Me(3)N·BH(2)SR (R = tBu [2a], nBu [2b], iPr [2c], Ph [2d], C(6)F(5) [2e]) have been prepared and characterized. Attempts to access secondary and primary amine adducts of thioboranes via amine-exchange reactions involving these species proved unsuccessful, with the thiolate moiety shown to be vulnerable to displacement by free amine. However, treatment of the arylthioboranes, [BH(2)-SPh](3) (9) and C(6)F(5)SBH(2)·SMe(2) (10) with Me(2)NH and iPr(2)NH successfully yielded the adducts Me(2)NH·BH(2)SR (R = Ph [11a], C(6)F(5) [12a]) and iPr(2)NH·BH(2)SR (R = Ph [11b], C(6)F(5) [12b]) in high yield. These adducts were also shown to be accessible via thermally induced hydrothiolation of the aminoboranes Me(2)N═BH(2), derived from the cyclic dimer [Me(2)N-BH(2)](2) (13), and iPr(2)N═BH(2) (14), respectively. Attempts to prepare the aliphatic thiolate substituted adducts R(2)NH·BH(2)SR' (R = Me, iPr; R' = tBu, nBu, iPr) via this method, however, proved unsuccessful, with the temperatures required to facilitate hydrothiolation also inducing thermal dehydrogenation of the amine-thioborane products to form aminothioboranes, R(2)N═BH(SR'). Thermal and catalytic dehydrogenation of the targeted amine-thioboranes, 11a/11b and 12a/12b were also investigated. Adducts 11b and 12b were cleanly dehydrogenated to yield iPr(2)N═BH(SPh) (22) and iPr(2)N═BH(SC(6)F(5)) (23), respectively, at 100 °C (18 h, toluene), with dehydrogenation also possible at 20 °C (42 h, toluene) with a 2 mol % loading of [Rh(μ-Cl)cod](2) in the case of the former species. Similar studies with adduct 11a evidenced a competitive elimination of H(2) and HSPh upon thermolysis, and other complex reactivity under catalytic conditions, whereas the fluorinated analogue 12a was found to be resistant to dehydrogenation.     

Iron complexes for the catalytic transfer hydrogenation of acetophenone: steric and electronic effects imposed by alkyl substituents at phosphorus

A series of iron(II) complexes, trans-[Fe(NCMe)(2)(PR(2)CH(2)CH═NCH(2)CH(2)N═CHCH(2)PR(2))][BPh(4)](2) (5, R = Cy; 7, R = iPr; 9, R = Et) were prepared via the template synthesis in one-pot involving air-stable phosphonium dimers, [cyclo-(-PR(2)CH(2)CH(OH)-)(2)](Br)(2) (4, R = Cy; 6, R = iPr; 8, R = Et), KOtBu, [Fe(H(2)O)(6)][BF(4)](2) and ethylenediamine in acetonitrile. In the synthesis of 9, a methanol/acetonitrile solvent mixture was required; otherwise an intermediate iron bis(tridentate) complex, [Fe(PEt(2)CH(2)CH═NCH(2)CH(2)NH(2))(2)](2+), formed as determined by electrospray ionization mass spectrometry (ESI-MS). The crude iron(II) complexes from a template synthesis with ethylenediamine or (S,S)-1,2-diphenylethylenediamine are stirred in acetone under a CO atmosphere (～2 atm) overnight to displace a NCMe ligand; however, in addition to this, bromide displaces an NCMe ligand as well to form a new class of the iron complexes trans-[Fe(CO)(Br)(PR(2)CH(2)CH═NCHR'CHR'N═CHCH(2)PR(2))](+) (10 R = Cy, R' = H; (S,S)-11, R = Cy, R' = Ph; 12, R = iPr, R' = H; (S,S)-13, R = iPr, R' = Ph; 14, R = Et, R' = H; (S,S)-15, R = Et, R' = Ph). These complexes were isolated in moderate yields (55-84%) as tetraphenylborate salts. Complexes 10-15 were tested for the catalytic transfer hydrogenation of acetophenone in basic iso-propanol at 25 and 50 °C. The complexes 10-13 (where R = Cy or iPr) were inactive while the complexes 14 and (S,S)-15 (where R = Et) were active at 25 °C but had better activity at 50 °C. Complex (S,S)-15 was higher in activity than complex 14, achieving turnover frequencies as high as 4100 h(-1), conversions of acetophenone to (R)-1-phenylethanol as high as 80% and an enantiomeric excess (e.e.) of 50% in the product. As catalysis progressed, the e.e. diminished to as low as 26%.     

Reactions of aliphatic ketones R2CO (R=Me, Et, iPr and tBu) with the MCI4/Li(Hg) system (M=U or Ti): mechanistic analogies between the McMurry, Wittig, and Clemmensen reactions

Analysis of the products of the reactions of ketones R2CO (R = Me, Et, iPr, tBu) with the MCl4/Li(Hg) system (M = U, Ti) at 20 degrees C revealed significant differences. For R = Me, the reaction proceeded exclusively (M = U) or preferentially (M = Ti) via a metallopinacol intermediate resulting from dimerization of ketyl radicals. Pinacol was liberated by hydrolysis, and tetramethylethylene was obtained after further reduction at 65 degrees C. For R=iPr, formation of iPr2C=CiPr2 as the only coupling product, the nonproduction of this alkene by reduction of the uranium pinacolate [U]-OCR2CR2O-[U] (R= iPr) at 20 degrees C, and the instability of the corresponding titanium pinacolate towards rupture of the pinacolic C-C bond indicated that reductive coupling of iPr2CO did not proceed by dimerization of ketyl radicals. Formation of 2,4-dimethyl-2-pentene was in favor of a carbenoid intermediate resulting from deoxygenative reduction of the ketyl. These results revealed that for sterically hindered ketones, McMurry reactions can be viewed as Wittig-like olefination reactions. For R=tBu, no coupling product was obtained and the alkane tBu2CH2 was the major product. The involvement of the carbenoid species [M]=CtBu2 was confirmed by its trapping with H2O, leading to tBu2CH2, and with the aldehydes RCHO, giving the cross-coupling products tBu2C=C(R)H (R = Me, tBu). Therefore, in the case of severely congested ketones, McMurry reactions present strong similarities to the Clemmensen reduction of ketones, owing to the involvement in both reactions of carbenoid species which exhibit similar reactivity.     

Sterically encumbered acyclic diphosphazanes: synthesis, conformations and coordination behavior

The reaction between lambda3-diphosphazane [EtN(PCl2)2] and the sodium salts of substituted phenols affords sterically encumbered diphosphazanes [EtN{P(OR)2}2] (R = -C6H3iPr2-2,6 (1), -C6H3Me2-2,6 (2) and -C6H2Me3-2,4,6 (3)). When the same reaction was carried out with bulky sodium 2,4-di-tert-butyl-4-methylphenoxide, only a monosubstitution takes place to result in the formation of [EtN{PCl(OR)}2] (R = -C6H2tBu2-2,6-Me-4) (4). Further reaction of 2 with [Mo(CO)4(NBD)] produces cis-[(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4] (5). Diphosphazanes 1-4 and the metal derivative 5 have been characterized by means of their analytical data and EI-MS, IR and multinuclear NMR (1H and 31P) spectral data. The solid-state structure of the diphosphazanes 1, 2 and 4, and the molybdenum complex 5 have been determined by X-ray diffraction studies. Irrespective of the size of substituent, the bulky groups on the phosphorus and nitrogen are on the same side of the P-N-P skeleton with a local C2v symmetry. The central nitrogen remains almost trigonal planar in all the compounds.     

Dichloro organosilicon bismuthanes as precursors for rare compounds with a bismuth-pnictogen or bismuth-tellurium bond

The chloro-bridged interpnictogen compounds [tBu?PhSiE{BiClCH(SiMe?)?}?] (E = P (4), As (5)) can be synthesized by the reaction of [tBu?PhSiELi?] (E = P (2), As (3)) with (Me?Si)?CHBiCl? in a molar ratio of 1?:?2. The reaction of iPr?SiAs(SiMe?)? with (Me?Si)?CHBiCl? yields the analogous compound [iPr?SiAs{BiClCH(SiMe?)?}?] (6) as well as the diarsine species [As{BiClCH(SiMe?)?}?]? (7). Preparation of 7 is also possible in the reaction of As(SiMe?)? with (Me?Si)?CHBiCl?. Starting from (Me?Si)?SiTeSiMe?, the Bi/Te compounds [{(Me?Si)?SiTe}?BiR] (R = CH(SiMe?)? (8), C(SiMe?)? (9)) are obtained by the reaction with RBiCl? (R = CH(SiMe?)?, C(SiMe?)? (1)). The intermediate and final products are characterized by multinuclear NMR spectroscopy and IR spectroscopy. Furthermore, crystal structures determined by X-ray diffraction are described for compounds 1 and 3-9.     

Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands

The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(N(t)Bu)][X] (BDI = [Ar]NC(CH(3))CHC(CH(3))N[Ar], Ar = 2,6-(i)Pr(2)C(6)H(3); M = Nb, Ta; X = MeB(C(6)F(5))(3), B(C(6)F(5))(4)] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R(3)PC(O)Me)M(N(t)Bu)][B(C(6)F(5))(4)] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me(2)-C(6)H(3)) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylN[double bond, length as m-dash]C(Me))Nb(N(t)Bu)][B(C(6)F(5))(4)], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe(2))Nb(N(t)Bu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph(3)SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.     

Synthesis and reactivity of calix[4]arene-supported group 4 imido complexes

New mononuclear titanium and zirconium imido complexes [M(NR)(R'(2)calix)] [M=Ti, R'=Me, R=tBu (1), R=2,6-C(6)H(3)Me(2) (2), R=2,6-C(6)H(3)iPr(2) (3), R=2,4,6-C(6)H(2)Me(3) (4); M=Ti, R'=Bz, R=tBu (5), R=2,6-C(6)H(3)Me(2) (6), R=2,6-C(6)H(3)iPr(2) (7); M=Zr, R'=Me, R=2,6-C(6)H(3)iPr(2) (8)] supported by 1,3-diorganyl ether p-tert-butylcalix[4]arenes (R'(2)calix) were prepared in good yield from the readily available complexes [MCl(2)(Me(2)calix)], [Ti(NR)Cl(2)(py)(3)], and [Ti(NR)Cl(2)(NHMe(2))(2)]. The crystallographically characterised complex [Ti(NtBu)(Me(2)calix)] (1) reacts readily with CO(2), CS(2), and p-tolyl-isocyanate to give the isolated complexes [Ti[N(tBu)C(O)O](Me(2)calix)] (10), [[Ti(mu-O)(Me(2)calix)](2)] (11), [[Ti(mu-S)(Me(2)calix)](2)] (12), and [Ti[N(tBu)C(O)N(-4-C(6)H(4)Me)](Me(2)calix)] (13). In the case of CO(2) and CS(2), the addition of the heterocumulene to the Ti-N multiple bond is followed by a cycloreversion reaction to give the dinuclear complexes 11 and 12. The X-ray structure of 13.4(C(7)H(8)) clearly establishes the N,N'-coordination mode of the ureate ligand in this compound. Complex 1 undergoes tert-butyl/arylamine exchange reactions to form 2, 3, [Ti(N-4-C(6)H(4)Me)(Me(2)calix)] (14), [Ti(N-4-C(6)H(4)Fc)(Me(2)calix)] (15) [Fc=Fe(eta(5)-C(5)H(5))(eta(5)-C(5)H(4))], and [[Ti(Me(2)calix)](2)[mu-(N-4-C(6)H(4))(2)CH(2)]] (16). Reaction of 1 with H(2)O, H(2)S and HCl afforded the compounds [[Ti(mu-O)(Me(2)calix)](2)] (11), [[Ti(mu-S)(Me(2)calix)](2)] (12), and [TiCl(2)(Me(2)calix)] in excellent yields. Furthermore, treatment of 1 with two equivalents of phenols results in the formation of [Ti(O-4-C(6)H(4)R)(2)(Me(2)calix)] (R=Me 17 or tBu 18), [Ti(O-2,6-C(6)H(3)Me(2))(2)(Me(2)calix)] (19) and [Ti(mbmp)(Me(2)calix)] (20; H(2)mbmp=2,2'-methylene-bis(4-methyl-6-tert-butylphenol) or CH(2)([CH(3)][C(4)H(9)]C(6)H(2)-OH)(2)). The bis(phenolate) compounds 17 and 18 with para-substituted phenolate ligands undergo elimination and/or rearrangement reactions in the nonpolar solvents pentane or hexane. The metal-containing products of the elimination reactions are dinuclear complexes [[Ti(O-4-C(6)H(4)R)(Mecalix)](2)] [R=Me (23) or tBu (24)] where Mecalix=monomethyl ether of p-tert-butylcalix[4]arene. The products of the rearrangement reaction are [Ti(O-4-C(6)H(4)Me)(2) (paco-Me(2)calix)] (25) and [Ti(O-4-C(6)H(4)tBu)(2)(paco-Me(2)calix)] (26), in which the metallated calix[4]arene ligand is coordinated in a form reminiscent of the partial cone (paco) conformation of calix[4]arene. In these compounds, one of the methoxy groups is located inside the cavity of the calix[4]arene ligand. The complexes 24, 25 and 26 have been crystallographically characterised. Complexes with sterically more demanding phenolate ligands, namely 19 and 20 and the analogous zirconium complexes [Zr(O-4-C(6)H(4)Me)(2)(Me(2)calix)] (21) and [Zr(O-2,6-C(6)H(3)Me(2))(2)(Me(2)calix)] (22) do not rearrange. Density functional calculations for the model complexes [M(OC(6)H(5))(2)(Me(2)calix)] with the calixarene possessing either cone or partial cone conformations are briefly presented.     

Preparation and characterization of the argentates: [Ag[P(CF(3))(2)](2)](-), [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-) (M = Cr, W), and [Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)](-): X-ray crystal structure of [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)

The first example of a mononuclear diphosphanidoargentate, bis[bis(trifluoromethyl)phosphanido]argentate, [Ag[P(CF(3))(2)](2)](-), is obtained via the reaction of HP(CF(3))(2) with [Ag(CN)(2)](-) and isolated as its [K(18-crown-6)] salt. When the cyclic phosphane (PCF(3))(4) is reacted with a slight excess of [K(18-crown-6)][Ag[P(CF(3))(2)](2)], selective insertion of one PCF(3) unit into each silver phosphorus bond is observed, which on the basis of NMR spectroscopic evidence suggests the [Ag[P(CF(3))P(CF(3))(2)](2)](-) ion. On treatment of the phosphane complexes [M(CO)(5)PH(CF(3))(2)] (M = Cr, W) with [K(18-crown-6)][Ag(CN)(2)], the analogous trinuclear argentates, [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-), are formed. The chromium compound [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)] crystallizes in a noncentrosymmetric space group Fdd2 (No. 43), a = 2970.2(6) pm, b = 1584.5(3) pm, c = 1787.0(4), V = 8.410(3) nm(3), Z = 8. The C(2) symmetric anion, [Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)](-), shows a nearly linear arrangement of the P-Ag-P unit. Although the bis(pentafluorophenyl)phosphanido compound [Ag[P(C(6)F(5))(2)](2)](-) has not been obtained so far, the synthesis of its trinuclear counterpart, [K(18-crown-6)][Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)], was successful.