From Sn(II) to Sn(IV): Enhancing Lewis Acidity Via Oxidation.

We demonstrate the increased Lewis acidity on going from Sn(II) to Sn(IV) by oxidizing TpMe2SnOTf (OTf = SO3CF3) to TpMe2SnF(OTf)2. Replacement of the fluoride ion in TpMe2SnF(OTf)2 by a triflate, resulting in TpMe2Sn(OTf)3 further enhances the Lewis acidity at tin. 119Sn NMR spectroscopy, modified Gutmann-Beckett test, computational analysis, and catalytic phosphine oxide deoxygenation support the claims.

Chemistry of group 5 metallaboranes with heterocyclic thiol ligands: a combined experimental and theoretical study.

Thermolysis of [(Cp*Nb)2(B2H6)2], 1b (Cp* = η5-C5Me5), with 2-mercaptobenzothiazole, C6H4NSCSH (MBT), and 2-mercaptobenzoxazole, C6H4NOCSH (MBO), yielded hydrogen substituted compounds 2 and 3 with a general formula [(Cp*Nb)2(B2H6)(B2H5L)] (2: L = C6H4NSCS and 3: L = C6H4NOCS). A similar reaction of 1b with Ph2Se2 yielded the monosubstituted derivative [(Cp*Nb)2(B2H6){B2H5(PhSe)}], 4. All further efforts towards persubstitution of 1b under various drastic conditions were unfruitful. In parallel, in an effort to find a better synthetic route to the known Ta-aziridine complex [Cp*TaBH(C7H4NS2)CH2S2NC6H4], Cp*TaCl4 was treated with a 2-mercaptobenzothiazolyl-based borate ligand Na[H2B(C6H4NSCS)2]. Surprisingly, the reaction led to the formation of the half-sandwich trichloroaryltantalum(v) complex [Cp*TaCl3{κ2-N,S-C6H4NSCS}], 5, containing a heterocyclic thiol ligand. Using an alternative method complex 5 was isolated in good yield when Cp*TaCl4 was treated with the potassium salt of 2-mercaptobenzothiazole K[C6H4NSCS]. All the compounds were characterized by 1H, 11B{1H}, and 13C{1H} NMR spectroscopy, and their structures were unequivocally established by crystallographic analysis.

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

A triple-decker complex of tungsten, [(Cp*W)2{µ-η6:η6-B4H4Co2(CO)5}(H)2] (1; Cp* = η5-C5Me5), with a planar middle deck has been isolated by thermolysis of an in situ formed intermediate from the reaction of Cp*WCl4 and LiBH4 with Co2(CO)8. In addition, we have also isolated another triple-decker complex, [(Cp*W)2{µ-η6:η6-B5H5Fe(CO)3}(H)2] (4), having a puckered central ring, from a similar reaction with Fe2(CO)9. Clusters 1 and 4 are unprecedented examples of a triple-decker complex having a 24-valence electron with bridging hydrogen atoms.

"Triple-Decker Sandwich" Containing Planar {B2E2Pd} Ring (E = S or Se).

In an effort to generate triple-decker complexes comprising a {PdCl2}moiety in the middle deck, we have explored the reactivity of [(Cp*M)2{µ-B2H2E2}], 1-4 (1: M = Co, E = S; 2: M = Co, E = Se; 3: M = Rh, E = Se; and 4: M = Ir, E = Se; Cp* = η5-C5Me5), with [PdCl2(COD)] (COD = 1,5-cyclooctadiene). The reactions led to the formation of a series of trinuclear heterometallic triple-decker complexes, [(Cp*M)2{µ-B2H2E2Pd(Cl)2}], 5-8 (5: M = Co, E = S; 6: M = Co, E = Se; 7: M = Rh, E = Se; and 8: M = Ir, E = Se). Formation of the complexes 5-8 occurred almost instinctively as a single product with the elimination of the COD ligand. These complexes are examples of novel triple-decker species having a planar bridging palladacycle ligand, in which the Pd metal exists as Pd(II) in an uncommon pseudo-octahedral environment with an elongated M-Pd bonding interaction. The new species, 5-8, have been characterized spectroscopically, and the structures of 5-7 were confirmed by single-crystal X-ray diffraction studies. The structure and bonding of these molecules were further analyzed with the help of density functional theory studies that found a strong electron donation from the B2E2 (E = S or Se) fragment of the middle ring to the axial metals, while a weak bonding interaction between group 9 metals and Pd.

Chalcogen Stabilized bis-Hydridoborate Complexes of Cobalt: Analogues of Tetracyclo[4.3.0.02,4 .03,5 ]nonane.

Treatment of Li[BH3 ER] (E=Se or Te, R=Ph; E=S, R=CH2 Ph) with [Cp*CoCl]2 led to the formation of hydridoborate complexes, [{CoCp*Ph}{Cp*Co}{µ-EPh}{µ-κ2 -E,H-EBH3 }], 1a and 1 b (1 a: E=Se; 1 b: E=Te) and a bis-hydridoborate species [Cp*Co{µ-κ2 -Se,H-SeBH3 }]2 , 2. All the complexes, 1 a, 1 b and 2 are stabilized by ß-agostic type interaction in which 1 b represents a novel bimetallic borate complex with a rare B-Te bond. QTAIM analysis furnished direct proof for the existence of a shared and dative B-chalcogen and Co-chalcogen interactions, respectively. In parallel to the formation of the hydridoborate complexes, the reactions also yielded tetracyclic species, [Cp*Co{κ3 -E,H,H-E(BH2 )2 -C5 Me5 H3 }], 3 a and 3 b (3 a: E=Se and 3 b: E=S), wherein the bridgehead boron atoms are surrounded by one chalcogen, one cobalt and two carbon atoms of a cyclopentane ring. Molecules 3 a and 3 b are best described as the structural mimic of tetracyclo[4.3.0.02,4 .03,5 ]nonane having identical structure and similar valence electron counts.

Polyhedral [M2B5] Metallaborane Clusters and Derivatives: An Overview of Their Structural Features and Chemical Bonding.

A large number of metallaborane clusters and their derivatives with various structural arrangements are known. Among them, M2B5 clusters and derivatives constitute a significant class. Transition metals present in these species span from group 4 to group 7. Their structure can vary from oblatonido, oblatoarachno, to arachno type open structures. Many of these clusters appear to be hypoelectronic and are often considered as 'rule breakers' with respect to the classical Wade-Mingos electron counting rules. This is due to their unique highly oblate (flattened) deltahedral structures featuring a cross-cluster M-M interaction. Many theoretical calculations were performed to elucidate their electronic structure and chemical bonding properties. In this review, the synthesis, structure, and electronic aspects of the transition metal M2B5 clusters known in the literature are discussed. The chosen examples illustrate how, in synergy with experiments, computational results can provide additional valuable information to better understand the electronic properties and electronic requirements which govern their architecture and thermodynamic stability.

Diborane(6) and Its Analogues Stabilized by Mono-, Bi-, and Trinuclear Group 7 Templates: Combined Experimental and Theoretical Studies.

Irradiation of [Re2(CO)10] in the presence of BH3·thf resulted in the formation of several rhenium diborane(6) species, for example, [{(OC)4Re}{Re(CO)3}2(µ3-η2:η2:η2-B2H6)(µ-H)], 1; [{(OC)4Re}2{Re(CO)3}(µ3-η2:η2:η1-B2H6)(µ-H)], 2; and [{(OC)4Re}2(µ-η2:η2-B2H6)], 3, comprising diverse coordination modes of the [B2H6]2- ligand. Compound 1 contains a tris(bidentate) [B2H6]2- unit, whereas 2 consists of an unsymmetrically bound [µ3-η2:η2:η1-B2H6]2- ligand. In contrast, the irradiation of [Mn2(CO)10] with BH3·thf yielded only the Mn analogue of 1, [{(OC)4Mn}{Mn(CO)3}2(µ3-η2:η2:η2-B2H6)(µ-H)], 1'. In an attempt to generate the bimetallic Mn-diborane(6), we have carried out the reaction of 1' with PCy3 under photolytic conditions. The reaction led to the formation of two single base stabilized unsymmetrical diborane(5) species, [{Mn(CO)3}{Mn(CO)2PCy3}(µ-η2:η2-B2H5·PCy3)(µ-H)], 4, and [{Mn(CO)2PCy3}(η3-B2H5·PCy3)], 5. As [B2H6]2- and [B2H5·PCy3]- are isoelectronic, the bondings in 4 and 5 are analogous to that of diborane(6) species 1-3. All the new species have been characterized spectroscopically, and their structures were further confirmed by single-crystal X-ray diffraction studies. DFT-type quantum chemical calculations were carried out that provided insight into the bonding interaction of [B2H6]2- and [B2H5·PCy3]- with the M(CO)n fragments.

Metal-Rich Oxametallaboranes of Group 5 Metals: Synthesis and Structure of a Face-Fused µ7-Boride Cluster.

Aerobic oxidation of metallaborane compounds is an unexplored field apart from the few reports on accidental oxidation leading to oxametallaboranes. An effective method for the synthesis of group 5 oxametallaboranes has been developed by the oxidation of [(Cp*M)2(B2H6)2] (M = Ta/Nb) (Cp* = η5-C5Me5). The reaction of [(Cp*M)2(B2H6)2] (M = Ta/Nb) with O2 gas at room temperature yielded oxametallaboranes [(Cp*M)2(B4H10O)] (for 1, M = Nb; for 2, M = Ta). Density functional theory calculations signify an increase in the HOMO-LUMO energy gap for 1 and 2 as compared to that for the parent metallaboranes, [(Cp*M)2(B2H6)2] (M = Ta/Nb). Reaction of 1 and 2 with [Ru3(CO)12] led to the isolation of fused metallaborane clusters [(Cp*Nb)2(B2H4O){Ru(CO)2}2(B2H4){Ru(CO)3}2{µ-H}4] (3) and [(Cp*Ta)2(B3H4O){Ru(CO)2}3{µ7-B}{µ-CO}2{µ-H}4] (4). The structure of 3 may be considered as a fusion of five subunits [two tetrahedra (Td), two square pyramids (sqp), and one trigonal bipyramid (tbp)]. One of the key features of cluster 4 is the presence of a µ7-boride atom that shares three cluster units (one monocapped trigonal prism and two Td). All the compounds have been characterized by mass spectrometry, infrared spectroscopy, and 1H, 13C, and 11B nuclear magnetic resonance spectroscopy, and the structural types were unequivocally established by crystallographic analysis of compounds 1, 3, and 4.

Hypoelectronic 8-11-Vertex Irida- and Rhodaboranes.

A series of novel isocloso-diiridaboranes [(Cp*Ir)2B6H6], 1, 2; [1,7-(Cp*Ir)2B8H8], 4; [1,4-(Cp*Ir)2B8H8], 5; [(Cp*Ir)2B9H9], 8; isonido-[(Cp*Ir)2B7H7], 3; and 10-vertex cluster [5,7-(Cp*Ir)2B8H12], 6 (Cp* = η(5)-C5Me5) have been isolated and structurally characterized from the pyrolysis of [Cp*IrCl2]2 and BH3·thf. On the other hand, the corresponding rhodium system afforded 10- and 11-vertices clusters [5-(Cp*Rh)B9H13)], 7, and [(Cp*Rh)2B9H9], 9, respectively. Clusters 1 and 2 are topological isomers. The geometry of 1 is dodecahedral, similar to that of its parent borane [B8H8](2-), in which two of the [BH] vertices are replaced by two [Cp*Ir] fragments. The geometry of 2 can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds 4 and 5 are 10-vertex isocloso clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal-metal bond in 5. The solid-state structures of 8 and 9 attain an 11-vertex geometry in which a unique six-membered B6H6 moiety is bonded to the metal center. In addition, quantum-chemical calculations have been used to provide further insight into the electronic structure and stability of the clusters. All the compounds have been characterized by IR and (1)H, (11)B, and (13)C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis.

New Trinuclear Complexes of Group†6, 8, and 9 Metals with a Triply Bridging Borylene Ligand.

Trinuclear complexes of group 6, 8, and 9 transition metals with a (µ3 -BH) ligand [(µ3 -BH)(Cp*Rh)2 (µ-CO)M'(CO)5 ], 3 and 4 (3: M'=Mo; 4: M'=W) and 5-8, [(Cp*Ru)3 (µ3 -CO)2 (µ3 -BH)(µ3 -E)(µ-H){M'(CO)3 }] (5: M'=Cr, E=CO; 6: M'=Mo, E=CO; 7: M'=Mo, E=BH; 8: M'=W, E=CO), have been synthesized from the reaction between nido-[(Cp*M)2 B3 H7 ] (nido-1: M=Rh; nido-2: M=RuH, Cp*=η(5) -C5 Me5 ) and [M'(CO)5 ⋅thf] (M'=Mo and W). Compounds 3 and 4 are isoelectronic and isostructural with [(µ3 -BH)(Cp*Co)2 (µ-CO)M'(CO)5 ], (M'=Cr, Mo and W) and [(µ3 -BH)(Cp*Co)2 (µ-CO)(µ-H)2 M''H(CO)3 ], (M''=Mn and Re). All compounds are composed of a bridging borylene ligand (B-H) that is effectively stabilized by a trinuclear framework. In contrast, the reaction of nido-1 with [Cr(CO)5 ⋅thf] gave [(Cp*Rh)2 Cr(CO)3 (µ-CO)(µ3 -BH)(B2 H4 )] (9). The geometry of 9 can be viewed as a condensed polyhedron composed of [Rh2 Cr(µ3 -BH)] and [Rh2 CrB2 ], a tetrahedral and a square pyramidal geometry, respectively. The bonding of 9 can be considered by using the polyhedral fusion formalism of Mingos. All compounds have been characterized by using different spectroscopic studies and the molecular structures were determined by using single-crystal X-ray diffraction analysis.

All-metallagermoxane with an adamantanoid cage structure: [(Cp*Ru(CO)2Ge)4(µ-O)6] (Cp* = η(5)-C5Me5).

In an attempt to synthesize a zero valent germanium compound, we have carried out the reaction of [(Cp*RuCO)(GeCl2)]2, 1 with potassium metal that led to the formation of a metallagermoxane [(Cp*Ru(CO)2Ge)4(µ-O)6], 2. Compound 2 is the first example of a tetrametallagermoxane with an exo-{Cp*Ru(CO)2} fragment. DFT calculations were used to examine the key intermediates associated with the formation of 2.