Synthesis and Reactions of a Hybrid Tristibine Ligand

The tripodal tristibine N­(CH₂-2-C₆H₄SbMe₂)₃ (L) has been prepared in high yield and characterized by ¹H and ¹³C­{¹H} NMR spectroscopy and elemental analysis. A range of reactions with transition-metal acceptors were carried out to probe the coordinative properties of L. The 3/1 M/L complex [{FeCp­(CO)₂}₃(L)-κ<i>Sb</i>:κ<i>Sb</i>′:κ<i>Sb</i>″]­[BF₄]₃ involves tridentate bridging coordination of L to three CpFe­(CO)₂ fragments. In [Mn­(CO)₃(L)]­[CF₃SO₃] the ligand adopts a tridentate chelating mode via a Sb₃ donor set; treatment of this complex with Me₃NO in MeCN solution gave crystals of [Mn­(CO)₂(L)­(MeCN)]­[CF₃SO₃], which lost MeCN in vacuo, probably resulting in coordination of CF₃SO₃^– coordination of the [CF₃SO₃]⁻ anion. [M­(L)]­[BF₄] (M = Ag, Cu) were also prepared. The reaction of L with CuBr leads to isolation of [Cu₄Br₄(L)₂] in the solid state, which contains a Cu₂Br₄ core with a short central Cu···Cu distance, capped with Cu­(L) units at each end. The transition-metal complexes of L were characterized by elemental analysis, ESI⁺ mass spectrometry, IR spectroscopy, and ¹H, ¹³C­{¹H}, and (where appropriate) ⁵⁵Mn or ⁶³Cu NMR spectroscopy. Solid-state X-ray structures were determined for [Mn­(CO)₃(L)]­[CF₃SO₃], [Mn­(CO)₂(L)­(MeCN)]­[CF₃SO₃], [Cu₄Br₄(L)₂], and [Cu₃Br₂(L)₂]­[BF₄]. In each of these structures the chelating ligand adopts a twisted, propeller-like conformation. NMR spectroscopic analysis suggests that the ligand also adopts this rigid conformation in solution

Trialkylstibine Complexes of Boron, Aluminum, Gallium, and Indium Trihalides: Synthesis, Properties, and Bonding

The reaction of BX₃ (X = Cl, Br, I) with SbR₃ (R = Et,ⁱPr) in anhydrous hexane or toluene produced moisture-sensitive [BX₃(SbR₃)], whose stability increases with halide: Cl < Br < I. Unstable [BF₃(SbR₃)] species were also characterized spectroscopically but lose BF₃ very readily. The [MX₃(SbR₃)] (M = Al, Ga, In) complexes were isolated from hexane solution; the Ga and In complexes can be recrystallized unchanged from CH₂Cl₂, but [AlX′₃(SbR₃)] (X′ = Br, I) undergoes X′/Cl exchange with the solvent. The new complexes were characterized by IR and multinuclear NMR spectroscopy (¹H, ¹³C­{¹H}, ¹¹B, ²⁷Al, ⁷¹Ga, ¹¹⁵In, as appropriate). X-ray crystal structures are reported for [BX₃(SbR₃)] (X = Br, I; R = Et, ⁱPr; X = Cl, R = ⁱPr), [AlI₃(SbⁱPr₃)], [GaX₃(SbR₃)] (X = Cl, I; R = ⁱPr), [GaBr₃(SbEt₃)], and [InX₃(SbR₃)] (X = Cl, I; R = Et, ⁱPr); all contain pseudotetrahedral geometries at both the group 13 and antimony atoms, and comparisons with phosphine and arsine analogues are discussed. The donor–acceptor bond lengths are unexceptional, but coordination of the stibine is accompanied by a significant widening of the C–Sb–C angles and a small reduction in C–Sb distances. DFT calculations confirm these results from significant changes in the antimony 5s and 5p contributions to the Sb–C bonds, with corresponding increases in the 5p character of the antimony-based “lone pair” on coordination. Intermolecular hypervalent Cl···Sb interactions are present in the two [InCl₃(SbR₃)] complexes but absent in the others

Phosphine and Diphosphine Complexes of Silicon(IV) Halides

The reaction of SiX₄ (X = Cl or Br) with PMe₃ in anhydrous CH₂Cl₂ forms <i>trans</i>-[SiX₄(PMe₃)₂], while the diphosphines, Me₂P­(CH₂)₂PMe₂, Et₂P­(CH₂)₂PEt₂, and <i>o</i>-C₆H₄(PMe₂)₂ form <i>cis</i>-[SiX₄(diphosphine)], all containing six-coordinate silicon centers. With Me₂PCH₂PMe₂ the product was <i>trans</i>-[SiCl₄(κ¹-Me₂PCH₂PMe₂)₂]. The complexes have been characterized by X-ray crystallography, microanalysis, IR, and multinuclear (¹H, ¹³C­{¹H}, and ³¹P­{¹H}) NMR spectroscopies. The complexes are stable solids and not significantly dissociated in nondonor solvents, although they are very moisture and oxygen sensitive. This stability conflicts with the predictions of recent density functional theory (DFT) calculations (Wilson et al.<i> Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) which suggested six-coordinate silicon phosphines would be unstable, and also contrasts with the failure to isolate complexes with SiF₄ (George et al.<i> Dalton Trans</i>. <b>2011</b>, <i>40,</i> 1584–1593). No reaction occurred between phosphines and SiI₄, or with SiX₄ and arsine ligands including AsMe₃ and <i>o</i>-C₆H₄(AsMe₂)₂. Attempts to make five-coordinate [SiX₄(PR₃)] using the sterically bulky phosphines, P^tBu₃, PⁱPr₃, or PCy₃ failed, with no apparent reaction occurring, consistent with predictions (Wilson et al. <i>Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) that such compounds would be very endothermic, while the large cone angles of the phosphines presumably preclude formation of six-coordination at the small silicon center. The reaction of Si₂Cl₆ with PMe₃ or the diphosphines in CH₂Cl₂ results in instant disproportionation to the SiCl₄ adducts and polychlorosilanes, but from hexane solution very unstable white [Si₂Cl₆(PMe₃)₂] and [Si₂Cl₆(diphosphine)] (diphosphine = Me₂P­(CH₂)₂PMe₂ or <i>o</i>-C₆H₄(PMe₂)₂) precipitate. The reactions of SiHCl₃ with PMe₃ and Me₂P­(CH₂)₂PMe₂ also produce the SiCl₄ adducts, but using Et₂P­(CH₂)₂PEt₂, colorless [SiHCl₃{Et₂P­(CH₂)₂PEt₂}] was isolated, which was characterized by an X-ray structure which showed a pseudo-octahedral complex with the Si–H <i>trans</i> to P. Attempts to reduce the silicon­(IV) phosphine complexes to silicon­(II) were unsuccessful, contrasting with the isolation of stable N-heterocyclic carbene adducts of Si­(II)

Phosphine and Diphosphine Complexes of Silicon(IV) Halides

The reaction of SiX₄ (X = Cl or Br) with PMe₃ in anhydrous CH₂Cl₂ forms <i>trans</i>-[SiX₄(PMe₃)₂], while the diphosphines, Me₂P­(CH₂)₂PMe₂, Et₂P­(CH₂)₂PEt₂, and <i>o</i>-C₆H₄(PMe₂)₂ form <i>cis</i>-[SiX₄(diphosphine)], all containing six-coordinate silicon centers. With Me₂PCH₂PMe₂ the product was <i>trans</i>-[SiCl₄(κ¹-Me₂PCH₂PMe₂)₂]. The complexes have been characterized by X-ray crystallography, microanalysis, IR, and multinuclear (¹H, ¹³C­{¹H}, and ³¹P­{¹H}) NMR spectroscopies. The complexes are stable solids and not significantly dissociated in nondonor solvents, although they are very moisture and oxygen sensitive. This stability conflicts with the predictions of recent density functional theory (DFT) calculations (Wilson et al.<i> Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) which suggested six-coordinate silicon phosphines would be unstable, and also contrasts with the failure to isolate complexes with SiF₄ (George et al.<i> Dalton Trans</i>. <b>2011</b>, <i>40,</i> 1584–1593). No reaction occurred between phosphines and SiI₄, or with SiX₄ and arsine ligands including AsMe₃ and <i>o</i>-C₆H₄(AsMe₂)₂. Attempts to make five-coordinate [SiX₄(PR₃)] using the sterically bulky phosphines, P^tBu₃, PⁱPr₃, or PCy₃ failed, with no apparent reaction occurring, consistent with predictions (Wilson et al. <i>Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) that such compounds would be very endothermic, while the large cone angles of the phosphines presumably preclude formation of six-coordination at the small silicon center. The reaction of Si₂Cl₆ with PMe₃ or the diphosphines in CH₂Cl₂ results in instant disproportionation to the SiCl₄ adducts and polychlorosilanes, but from hexane solution very unstable white [Si₂Cl₆(PMe₃)₂] and [Si₂Cl₆(diphosphine)] (diphosphine = Me₂P­(CH₂)₂PMe₂ or <i>o</i>-C₆H₄(PMe₂)₂) precipitate. The reactions of SiHCl₃ with PMe₃ and Me₂P­(CH₂)₂PMe₂ also produce the SiCl₄ adducts, but using Et₂P­(CH₂)₂PEt₂, colorless [SiHCl₃{Et₂P­(CH₂)₂PEt₂}] was isolated, which was characterized by an X-ray structure which showed a pseudo-octahedral complex with the Si–H <i>trans</i> to P. Attempts to reduce the silicon­(IV) phosphine complexes to silicon­(II) were unsuccessful, contrasting with the isolation of stable N-heterocyclic carbene adducts of Si­(II)

Trialkylstibine Complexes of Boron, Aluminum, Gallium, and Indium Trihalides: Synthesis, Properties, and Bonding

The reaction of BX₃ (X = Cl, Br, I) with SbR₃ (R = Et,ⁱPr) in anhydrous hexane or toluene produced moisture-sensitive [BX₃(SbR₃)], whose stability increases with halide: Cl < Br < I. Unstable [BF₃(SbR₃)] species were also characterized spectroscopically but lose BF₃ very readily. The [MX₃(SbR₃)] (M = Al, Ga, In) complexes were isolated from hexane solution; the Ga and In complexes can be recrystallized unchanged from CH₂Cl₂, but [AlX′₃(SbR₃)] (X′ = Br, I) undergoes X′/Cl exchange with the solvent. The new complexes were characterized by IR and multinuclear NMR spectroscopy (¹H, ¹³C­{¹H}, ¹¹B, ²⁷Al, ⁷¹Ga, ¹¹⁵In, as appropriate). X-ray crystal structures are reported for [BX₃(SbR₃)] (X = Br, I; R = Et, ⁱPr; X = Cl, R = ⁱPr), [AlI₃(SbⁱPr₃)], [GaX₃(SbR₃)] (X = Cl, I; R = ⁱPr), [GaBr₃(SbEt₃)], and [InX₃(SbR₃)] (X = Cl, I; R = Et, ⁱPr); all contain pseudotetrahedral geometries at both the group 13 and antimony atoms, and comparisons with phosphine and arsine analogues are discussed. The donor–acceptor bond lengths are unexceptional, but coordination of the stibine is accompanied by a significant widening of the C–Sb–C angles and a small reduction in C–Sb distances. DFT calculations confirm these results from significant changes in the antimony 5s and 5p contributions to the Sb–C bonds, with corresponding increases in the 5p character of the antimony-based “lone pair” on coordination. Intermolecular hypervalent Cl···Sb interactions are present in the two [InCl₃(SbR₃)] complexes but absent in the others

Halostibines SbMeX₂ and SbMe₂X: Lewis Acids or Lewis Bases?

Alkylhalostibines have been shown to behave either as Lewis acids toward appropriate neutral ligands or as Lewis bases to low-valent metal fragments. The boundaries of their Lewis acid and Lewis base behavior have been determined, and the structural and spectroscopic consequences of the different behaviors probed. [SbMeX₂(L–L)] (L–L = 2,2′-bipyridyl, 1,10-phenanthroline) and [SbMeX₂(L)₂] (L = OPMe₃, OPPh₃) are five-coordinate, distorted square-pyramidal monomers with the Me group axial, with the bond distances little affected by coordination. Significant changes in the bonding within the group 6 carbonyl complexes [M­(CO)₅(L′)] are evident, with L′→M σ-donation decreasing across the series L′ = SbMe₃ → SbMe₂Br → SbMeBr₂, and an increase in M→L′ π-acceptance within the same series. Intermolecular interactions are a major feature within these systems, ranging from weak, MCO···Sb interactions in [M­(CO)₅(SbMe₂Br)] and [M­(CO)₅(SbMeBr₂)] to remarkably strong O···Sb hypervalent bonds in [Mn­(CO)₅(SbMe₂Br)]­[CF₃SO₃] and [Mn­(CO)₃(SbMe₂Br)₃]­[CF₃SO₃], the latter involving the triflate anions. These lead to large changes in the geometry at Sb and represent very rare examples in which the antimony exhibits significant Lewis acid and Lewis base behavior simultaneously. The coordinated alkylhalostibines are alkylated cleanly with MeLi or ⁿBuLi

Rare Neutral Diphosphine Complexes of Scandium(III) and Yttrium(III) Halides

Reaction of Me₂PCH₂CH₂PMe₂ or <i>o</i>-C₆H₄(PMe₂)₂ (L–L) with a suspension of ScI₃ or YI₃ in MeCN solution under rigorously anhydrous and oxygen-free conditions produced the highly unusual complexes [ScI₃(L–L)₂], [YI₃(Me₂PCH₂CH₂PMe₂)₂], and [YI₃{<i>o</i>-C₆H₄(PMe₂)₂}₂MeCN]. X-ray crystal structures reveal that the scandium complexes adopt seven-coordinate, pentagonal-bipyramidal geometries with chelating diphosphines, while the eight-coordinate [YI₃{<i>o</i>-C₆H₄(PMe₂)₂}₂MeCN] is dodecahedral. The complexes were characterized by microanalysis and IR and multinuclear NMR spectroscopy. Solid-state NMR data (⁴⁵Sc, ⁸⁹Y, ³¹P) and variable-temperature solution NMR data (¹H, ³¹P­{¹H}, ⁴⁵Sc) are presented and compared, leading to the conclusion that the same species are present in both the solid state and CH₂Cl₂ solution. Attempts to prepare complexes with other scandium halides and with aryl diphosphines and <i>o</i>-C₆H₄(AsMe₂)₂ are briefly described

Complexes of molybdenum(VI) oxide tetrafluoride and molybdenum(VI) dioxide difluoride with neutral N- and O-donor ligands

[MoOF 4 (MeCN)], prepared from reaction of MoF 6 with (Me 3 Si) 2 O in anhydrous MeCN solution, reacts with the neutral O-donor ligands, thf, Ph 3 PO, Me 3 PO, dmf and dmso, (L) in a 1:1 molar ratio under rigorously anhydrous conditions to form six-coordinate [MoOF 4 (L)], which have been characterised by microanalysis, IR, 1 H, 19 F{ 1 H} and 95 Mo NMR spectroscopy. In the presence of moisture the major products are [MoO 2 F 2 (L) 2 ], which can be made directly by reaction of [MoOF 4 (L)] with a further equivalent of L and (Me 3 Si) 2 O. [MoOF 4 (MeCN)] and 2,2′-bipyridyl produce the insoluble [MoOF 4 (bipy)], which is probably 7-coordinate. Ph 3 AsO is quantitatively converted to Ph 3 AsF 2 by [MoOF 4 (MeCN)], and soft ligands, including Me 2 S, Me 3 P and Me 3 As, reduce the oxide fluoride on contact. Unstable [MoO 2 F 2 (MeCN) 2 ] has also been prepared and the X-ray structure of [MoO 2 F 2 (MeCN) 2 ]·MeCN is reported. X-ray crystal structures are reported for [MoOF 4 (Ph 3 PO)], [MoO 2 F 2 (Ph 3 PO) 2 ], [MoO 2 F 2 (Me 3 PO)(H 2 O)] and [Mo 2 O 4 F 2 (μ-F) 2 (Me 3 PO) 2 ]. Comparisons with the corresponding chemistries of WOF 4 and WO 2 F 2 are described

Rare Neutral Diphosphine Complexes of Scandium(III) and Yttrium(III) Halides

Reaction of Me₂PCH₂CH₂PMe₂ or <i>o</i>-C₆H₄(PMe₂)₂ (L–L) with a suspension of ScI₃ or YI₃ in MeCN solution under rigorously anhydrous and oxygen-free conditions produced the highly unusual complexes [ScI₃(L–L)₂], [YI₃(Me₂PCH₂CH₂PMe₂)₂], and [YI₃{<i>o</i>-C₆H₄(PMe₂)₂}₂MeCN]. X-ray crystal structures reveal that the scandium complexes adopt seven-coordinate, pentagonal-bipyramidal geometries with chelating diphosphines, while the eight-coordinate [YI₃{<i>o</i>-C₆H₄(PMe₂)₂}₂MeCN] is dodecahedral. The complexes were characterized by microanalysis and IR and multinuclear NMR spectroscopy. Solid-state NMR data (⁴⁵Sc, ⁸⁹Y, ³¹P) and variable-temperature solution NMR data (¹H, ³¹P­{¹H}, ⁴⁵Sc) are presented and compared, leading to the conclusion that the same species are present in both the solid state and CH₂Cl₂ solution. Attempts to prepare complexes with other scandium halides and with aryl diphosphines and <i>o</i>-C₆H₄(AsMe₂)₂ are briefly described

Systematics of BX₃ and BX₂⁺ Complexes (X = F, Cl, Br, I) with Neutral Diphosphine and Diarsine Ligands

The coordination chemistry of the neutral diphosphines, R₂P­(CH₂)₂PR₂ (R = Me or Et) and <i>o</i>-C₆H₄(PR′₂)₂ (R′ = Me or Ph), and the diarsine, <i>o</i>-C₆H₄(AsMe₂)₂, toward the Lewis acidic BX₃ (X = F, Cl, Br, and I) fragments is reported, including several rare complexes incorporating BF₃ and BF₂⁺. The studies have revealed that the flexible dimethylene linked diphosphines form [(BX₃)₂{μ-R₂P­(CH₂)₂­PR₂}] exclusively, confirmed by multinuclear NMR (¹H, ¹¹B, ¹⁹F­{¹H}, and ³¹P­{¹H}) and IR spectroscopy and microanalytical data. Crystallographic determinations of the four BX₃ complexes with Et₂P­(CH₂)₂PEt₂ confirm the 2:1 stoichiometry and, taken together with the spectroscopic data, reveal that the Lewis acid behavior of the BX₃ fragment toward phosphine ligands increases in the order F ≪ Cl ∼ Br < I. The first diphosphine- and diarsine-coordinated dihaloboronium cations, [BX₂{<i>o</i>-C₆H₄(EMe₂)₂}]⁺ (E = P, As), are obtained using the rigid, preorganized <i>o</i>-phenylene linkages. These complexes are characterized similarly, and the data indicate that the complexes with <i>o</i>-C₆H₄(AsMe₂)₂ are much more labile and readily decomposed than the phosphine analogues. X-ray crystallographic studies on [BX₂{<i>o</i>-C₆H₄­(PMe₂)₂}]­[BX₄] (X = Cl, Br), [BI₂{<i>o</i>-C₆H₄­(PMe₂)₂}]­[I₃], and [BCl₂{<i>o</i>-C₆H₄­(AsMe₂)₂}]­[BCl₄] confirm the presence of distorted tetrahedral coordination at boron through a chelating diphosphine or diarsine and two X ligands, with <i>d</i>(B–P) revealing a similar increase in Lewis acidity down group 17. Comparison of <i>d</i>(B–P) and <i>d</i>(B–As) reveals an increase of <i>ca</i>. 0.08 Å from P to As. Reaction of BCl₃ with the diphosphine dioxide Ph₂P­(O)­CH₂P­(O)­Ph₂ gives the ligand-bridged dimer [(BCl₃)₂{Ph₂P­(O)­CH₂­P­(O)­Ph₂}], while using either BF₃ gas or [BF₃(SMe₂)] gives a mixture containing both [(BF₃)₂{μ-Ph₂P­(O)­CH₂P­(O)­Ph₂}] and the unexpected difluoroboronium salt, [BF₂{Ph₂P­(O)­CH₂P­(O)­Ph₂}]­[B₂F₇] containing a chelating phosphine oxide. The structure of the latter was confirmed crystallographically