Use of Single-Metal Fragments for Cluster Building Synthesis, Structure, and Bonding of Heterometallaboranes

International audienceThe synergic property of the CO ligand, in general, can stabilize metal complexes at lower oxidation states. Utilizing this feature of the CO ligand, we have recently isolated and structurally characterized a highly fluxional molybdenum complex [{Cp*Mo(CO)}{μ-ηη-BH}] (2; Cp* = η-CMe) comprising the diborane(4) ligand. Compound 2 represents a rare class of bimetallic diborane(4) complex corresponding to a singly bridged C structure. In an attempt to isolate the tungsten analogue of 2, [{Cp*W(CO)}{μ-ηη-BH}], we have isolated a rare vertex-fused cluster, [(Cp*W)WBH] (5). Having a structural likeness with the dimolybdenum alkyne complex [{CpMo(CO)}CH], we have further explored the chemistry of 2 with CO gas that yielded a homoleptic trimolybdenum complex, [(Cp*Mo)(μ-H)(μ-H)(μ-CO)BH] (4). In an attempt to replace the 16-electron {Cp*MoH(CO)} moiety in 4 with isolobal fragment {W(CO)}, we treated the intermediate, obtained from the reaction of Cp*MoCl and LiBH, with the monometal carbonyl fragment {W(CO)·THF}. The reaction indeed yielded two bimetallic clusters, [(Cp*Mo)BHW(CO)] (7) and [(Cp*Mo)BHW(CO)] (8), that seem to have been generated by the replacement of one {BH} or {BH} vertex from [(Cp*Mo)BH], respectively. All of the compounds have been characterized by various spectroscopic analyses and single-crystal X-ray diffraction studies. Electron-counting rules and molecular orbital analyses provided further insight into the electronic structure of all of these molecules

Triple-Decker Sandwich Complexes of Tungsten with Planar and Puckered Middle Decks

International audienceA triple-decker complex of tungsten, [(Cp*W){μ-η:η-BHCo(CO)}(H)] (; Cp* = η-CMe), with a planar middle deck has been isolated by thermolysis of an in situ formed intermediate from the reaction of Cp*WCl and LiBH with Co(CO). In addition, we have also isolated another triple-decker complex, [(Cp*W){μ-η:η-BHFe(CO)}(H)] (), having a puckered central ring, from a similar reaction with Fe(CO). Clusters and are unprecedented examples of a triple-decker complex having a 24-valence electron with bridging hydrogen atoms

Heterometallic boride clusters synthesis and characterization of butterfly and square pyramidal boride clusters

International audienceA number of heterometallic boride clusters have been synthesized and structurally characterized using various spectroscopic and crystallographic analyses. Thermolysis of [Ru-3(CO)(12)] with [Cp*WH3(B4H8)] (1) yielded [{Cp* W(CO)(2)}(2)(mu(4)-B){Ru(CO)(3)}(2)(mu-H)] (2), [{Cp*W(CO)(2)}(2) (mu(5) -B){Ru(CO)(3)}(2){Ru(CO)(2)}(mu-H)] (3), [{Cp*W(CO)(2)}(mu(5)-B){Ru(CO)(3)}(4)] (4) and a ditungstaborane cluster [(Cp*W)(2)B4H8Ru(CO)(3)] (5) (Cp*=eta(5)-C5Me5). Compound 2 contains 62 cluster valence-electrons, in which the boron atom occupies the semi-interstitial position of a M-4-butterfly core, composed of two tungsten and two ruthenium atoms. Compounds 3 and 4 can be described as hetero-metallic boride clusters that contain 74-cluster valence electrons (cve), in which the boron atom is at the basal position of the M-5-square pyramidal geometry. Cluster 5 is analogous to known [(Cp*W)(2)B5H9] where one of the BH vertices has been replaced by isolobal {Ru(CO)(3)} fragment. Computational studies with density functional theory (DFT) methods at the B3LYP level have been used to analyze the bonding of the synthesized molecules. The optimized geometries and computed B-11 NMR chemical shifts satisfactorily corroborate with the experimental data. All the compounds have been characterized by mass spectrometry, IR, H-1, B-11 and C-13 NMR spectroscopy, and the structural architectures were unequivocally established by crystallographic analyses of clusters 2-5

Combined Experimental and Theoretical Investigations of Group 6 Dimetallaboranes [(Cp*M)₂B₄H₁₀] (M = Mo and W)

Thermolysis of mono metal carbonyl fragment, [M′(CO)₅·thf, M′ = Mo and W, thf = tetrahydrofuran] with an <i>in situ</i> generated intermediate, obtained from the reaction of [Cp*MCl₄] (M = Mo and W, Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) with [LiBH₄·thf], yielded dimetallaboranes, <b>1</b> and <b>2</b>. Isolations of [{Cp*M­(CO)}₂B₄H₆] (M = Mo (<b>1</b>) and W­(<b>2</b>)) provide direct evidence for the existence of saturated molybdaborane and tungstaborane clusters, [(Cp*M)₂B₄H₁₀]. Our extensive theoretical studies together with the experimental observation suggests that the intermediate may be a saturated cluster [(Cp^#M)₂B₄H₁₀], not unsaturated [(Cp^#M)₂B₄H₈] (Cp^# = Cp or Cp*), which was proposed earlier by Fehlner. Furthermore, in order to concrete our findings, we isolated and structurally characterized analogous clusters [(Cp*Mo)₂(CO)­(μ-Cl)­B₃H₄W­(CO)₄] (<b>3</b>) and [(Cp*WCO)₂(μ-H)₂B₃H₃W­(CO)₄] (<b>4</b>). All the compounds have been characterized by solution-state ¹H, ¹¹B, IR, and ¹³C NMR spectroscopy, mass spectrometry, and the structural architectures of <b>1</b>, <b>3</b>, and <b>4</b> were unequivocally established by X-ray crystallographic analysis. The density functional theory calculations yielded geometries that are in close agreement with the observed structures. Both the Fenske–Hall and Kohn–Sham molecular orbital analyses showed an increased thermodynamic stability for [(Cp^#M)₂B₄H₁₀] compared to [(Cp^#M)₂B₄H₈]. Furthermore, large HOMO–LUMO gap and significant cross cluster M–M bonding have been observed for clusters <b>1</b>–<b>4</b>

Combined Experimental and Theoretical Investigations of Group 6 Dimetallaboranes [(Cp*M)₂B₄H₁₀] (M = Mo and W)

Thermolysis of mono metal carbonyl fragment, [M′(CO)₅·thf, M′ = Mo and W, thf = tetrahydrofuran] with an <i>in situ</i> generated intermediate, obtained from the reaction of [Cp*MCl₄] (M = Mo and W, Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) with [LiBH₄·thf], yielded dimetallaboranes, <b>1</b> and <b>2</b>. Isolations of [{Cp*M­(CO)}₂B₄H₆] (M = Mo (<b>1</b>) and W­(<b>2</b>)) provide direct evidence for the existence of saturated molybdaborane and tungstaborane clusters, [(Cp*M)₂B₄H₁₀]. Our extensive theoretical studies together with the experimental observation suggests that the intermediate may be a saturated cluster [(Cp^#M)₂B₄H₁₀], not unsaturated [(Cp^#M)₂B₄H₈] (Cp^# = Cp or Cp*), which was proposed earlier by Fehlner. Furthermore, in order to concrete our findings, we isolated and structurally characterized analogous clusters [(Cp*Mo)₂(CO)­(μ-Cl)­B₃H₄W­(CO)₄] (<b>3</b>) and [(Cp*WCO)₂(μ-H)₂B₃H₃W­(CO)₄] (<b>4</b>). All the compounds have been characterized by solution-state ¹H, ¹¹B, IR, and ¹³C NMR spectroscopy, mass spectrometry, and the structural architectures of <b>1</b>, <b>3</b>, and <b>4</b> were unequivocally established by X-ray crystallographic analysis. The density functional theory calculations yielded geometries that are in close agreement with the observed structures. Both the Fenske–Hall and Kohn–Sham molecular orbital analyses showed an increased thermodynamic stability for [(Cp^#M)₂B₄H₁₀] compared to [(Cp^#M)₂B₄H₈]. Furthermore, large HOMO–LUMO gap and significant cross cluster M–M bonding have been observed for clusters <b>1</b>–<b>4</b>

Synthesis and characterization of group 6-9 metal-rich homo- and hetero-metallaboranes

International audienceTo isolate the metal-rich metallaboranes of group 6-9, we have performed the reaction of various reaction intermediates, generally synthesized from the low-temperature reactions of [Cp∗WCl4] (Cp∗ ​= ​η5-C5Me5), [(Cp∗RhCl2)2], or [(Cp∗RuCl2)2] and [LiBH4 THF] with different transition metal carbonyl compounds. For example, the thermolytic reaction of [Fe2(CO)9] with an in situ generated intermediate, produced from the reaction of [Cp∗WCl4] and [LiBH4THF] afforded a trigonal bipyramidal cluster, [(μ3-BH)2H2{Cp∗W(CO)2}{Cp∗W(CO)}{Fe(CO)3}], 1 which contains a triply-bridging bis-{hydrido(borylene)} ligand. Similarly, the reaction of [Co2(CO)8] with nido-[(RhCp∗)2(B3H7)] I at room temperature, yielded an octahedral cluster, [(Cp∗Rh)2B2H2Co2(CO)5(μ3-CO)], 2. In this reaction, nido-I having (n+2) skeletal electron pairs (SEP) goes on for the formation of a closo-rhodaborane with (n+1) SEP. In addition, we have isolated a trinuclear bis(μ3-oxo) metalla cluster [(Cp∗Ru)3(μ3-OBF3)2(μ-H)], 3. Compound 3 can be considered as cluster having trigonal bipyramidal geometry with exo-BF3 fragment. All these clusters were characterized by IR, mass spectrometry, NMR, and single-crystal X-ray crystallographic analysis

Triple-decker complexes comprising heterocyclic middle-deck with coinage metals

International audienceEarlier accounts of triple-decker complexes comprising main group elements and transition metals in the middle-deck, motivated us to synthesize triple-decker complexes containing coinage metals in the middle-deck. As a result, we have explored the reactivity of open-cage nido - [(Cp *M) 2 { mu-B 2 H 2 E 2 }], 1 -3 (Cp * = eta 5 -C 5 Me 5 , 1 : M = Co, E = S ; 2 : M = Co, E = Se; 3 : M = Rh, E = Se) with [CuBr(SMe 2 )]. All the reactions yielded triple-decker complexes, [(Cp *M) 2 { mu-B 2 H 2 E 2 CuBr}], 4 -6 ( 4 : M = Co, E = S ; 5 : M = Co, E = Se; 6 : M = Rh, E = Se) having [CuBr] in the middle-deck. The removal of the SMe 2 ligand resulted in the formation of complexes 4 -6 as a single product. These complexes are examples of triple-decker species having a planar 5-membered [B 2 E 2 Cu] (E = S or Se) middle deck, in which the Cu exists as Cu(I) with an elongated M-Cu bonding interaction. Synthesized complexes have been established by ESI-MS, multinuclear nuclear magnetic resonance (NMR), and IR spectroscopy. The solid-state structures of 5 and 6 were confirmed by single-crystal X-ray diffraction analyses. Density functional theory (DFT) analyses of these complexes have presented a high electron donation from the [B 2 E 2 ] (E = S or Se) fragment of the middle ring to the axial metals and a weak bonding interaction between group 9 metals and Cu

Structures and Bonding of Early Transition Metallaborane Clusters

International audienceStructures and bonding of various homo-and heterometallic metallaborane clusters are described, which are stabilized in the coordination sphere of early transition metals. For example, the bimetallic triborane species [{Cp*Mo(CO)}2{?????13:13-B3H7}], 2, has been synthesized from the pyrolysis of an in situ generated intermediate, produced from the reaction of [Cp*Mo(CO)3Me], 1, and [LiBH4??THF] with an excess amount of [BH3?? THF]. Superficially cluster 2 is isostructural but not isoelectronic with [(Cp*MoCl)2B3H7] (I). Both clusters 2 and I contain a bimetallic template bridged by {B3H7} moiety. Cluster 2 is denoted as a unique saturated and unsubstituted closo bimetallic B3H7 cluster. Theoretical output implies that saturation in such clusters brings thermodynamic stability. Further, we have developed a new strategy for the synthesis of various heterometallic metal-rich metallaborane clusters. For example, pyrolysis of an intermediate, obtained from the reaction of [Cp*MoCl4], 4, and [LiBH4??THF] with cobalt and iron carbonyl compounds yielded triply bridging hydrido(hydroborylene), [{Cp*Mo(CO)2}2Co(CO)3BH(??-H)], 5, tetrametallic ??4- boride, [{Cp*Mo(CO)2}2(??4-B)(??-H){Co2(CO)5}], 6, triple decker complex, [(Cp*Mo)2{?????16:16-B4H4Co2(CO)5}(??-H)2], 7, metal-rich dimolybdaborane cluster, [(Cp*Mo)2Co2 (CO)3(??-CO)3B3H3(??-H)2], 8, and mixed-metal cluster, [(Cp*Mo)2B4H8Fe-(CO)3], 9. All the molecules have been characterized by1H, 11B{1H}, and 13C{1H} NMR spectroscopy, mass spectrometry, infrared (IR) spectroscopy, and single-crystal X-ray diffraction studies for clusters 2 and 5???9. The electron counting rules and density functional theory (DFT) calculations provided further insight into the bonding and electronic structures of these clusters. &lt;comment&gt;Superscript/Subscript Available&lt;/commen

Heterometallic Triply-Bridging Bis-Borylene Complexes

International audienceTriply-bridging bis-{hydrido(borylene)} and bis-borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe-2(CO)(9)] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl4] (Cp*=eta(5)-C5Me5) and [LiBH4.THF] afforded triply-bridging bis-{hydrido(borylene)}, [(mu(3)-BH)(2)H-2{Cp*W(CO)(2)}(2){Fe(CO)(2)}] (1) and bis-borylene, [(mu(3)-BH)(2){Cp*W(CO)(2)}(2){Fe(CO)(3)}] (2). The chemical bonding analyses of 1 show that the B-H interactions in bis-{hydrido (borylene)} species is stronger as compared to the M-H ones. Frontier molecular orbital analysis shows a significantly larger energy gap between the HOMO-LUMO for 2 as compared to 1. In an attempt to synthesize the ruthenium analogue of 1, a similar reaction has been performed with [Ru-3(CO)(12)]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(mu(3)-BH)(2){WCp*(CO)(2)}(2){Ru(CO)(3)}] (2 '), an analogue of 2. In search for the isolation of bridging bis-borylene species of Rh, we have treated [Co-2(CO)(8)] with nido-[(RhCp*)(2)(B3H7)], which afforded triply-bridging bis-borylene species [(mu(3)-BH)(2)(RhCp*)(2)Co-2(CO)(4)(mu-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; H-1, B-11, C-13 NMR spectroscopy; IR spectroscopy and mass spectrometry