Search

Several early-late heterodimetallaborane clusters have been isolated and structurally characterized through spectroscopic and crystallographic analysis. The thermolysis of [Cp2Zr(BH4)2] (Cp = η5-C5H5) with [Cp*IrB3H9] (Cp* = η5-C5Me5) and [(Cp*Rh)2B2H6] yielded arachno-[(Cp2Zr)(Cp*Ir)B3H9] ( 2) and arachno-[(Cp2Zr)(Cp*Rh)B4H10] ( 4), respectively. In a similar fashion, the reaction of [Cp2Hf(BH4)2] was performed with the same set of group 9 metallaboranes that led to the formation of arachno-[(Cp2Hf)(Cp*M′)B4H10] ( 5: M′ = Ir; 6: M′ = Rh). To the best of our knowledge, 2 is the first structurally characterized pentaborane(11) analogue containing zirconium, while the clusters 5 and 6 are the first examples with Hf in a hexaborane(12) core. The bonding between the Zr atoms and the boron ring was studied computationally by DFT methods, and 2 can be defined as a dimetallic analogue of arachno-B5H11 on the basis of the combined experimental and computational results. [ABSTRACT FROM AUTHOR]

Chloro-rhodaboratrane [(Cp*Rh)(L 2 )BCl] 4 has been synthesized from rhodium N,S-heterocyclic carbene complex [(Cp*Rh)(L 2 )(1-benzothiazol-2-ylidene)], 1 , (L = C 7 H 4 NS 2 ) and borane reagent BHCl 2 .SMe 2 . The Rh B bond in 4 is buttressed between two benzothiazolyl units in [3.3.0] fashion. The presence of B Cl bond allowed us to explore the chemistry of boratrane 4 at the boron centre. The reaction of ethynylmagnesium bromide with 4 yielded η 1 -vinyl complex [Cp*RhBr(C 2 H 2 )L] 5 , containing a five membered metallaheterocycle. In an objective to abstract the chloride, alike borylene synthesis from haloboryl, we performed the reaction of 4 with NaBAr F 4 that resulted the thiolato bridged bimetallic compound [Cp*Rh(μ-L) 3 RhCp*][BAr F 4 ] 6 (Ar F : C 6 H 3 (CF 3 ) 2 -3,5). [ABSTRACT FROM AUTHOR]

In a quest for effective synthetic precursors for the preparation of B-agostic complexes of ruthenium, we have shown that the reaction of [Cp*RuCl 2 ] 2 (Cp* = η5-C 5 Me 5 ) with [NaBt] or [NaBo] (Bt = dihydrobis(2-mercaptobenzthiazolyl)borate; Bo = dihydrobis(2-mercaptobenzoxazolyl)borate) led to the formation of B-agostic complexes [Cp*RuBH 2 L 2 ], 1a,b ( 1a : L = 2-mercaptobenzthiazol, 1b : L = 2-mercaptobenzoxazol) and [Cp*RuBH 3 L], 2a,b ( 2a : L = 2-mercaptobenzthiazol, 2b : L = 2-mercaptobenzoxazol) in good yields. In parallel to the formation of 1a,b and 2a,b , this method also allowed the formation of ruthenium hydrotrisborate complexes [Cp*RuBYL 3 ], 3a–c ( 3a : L = 2-mercaptobenzthiazol, Y = H; 3b : L = 2-mercaptobenzoxazol, Y = H; 3c : L = 2-mercaptobenzoxazol, Y = Cl). The key feature of complexes 3a–c is the coordination of one of the 2-mercaptobenzothiazole ligand that connects to the metal and the boron centre through a common sulfur atom. Upon heating, compounds 3a,b change into their corresponding S→N linkage isomers, in which the boron atom is bonded to three nitrogen atoms. The cyclic voltammetric studies on compounds 3a–c and 4a,b suggest that a deviation in coordination of the ligand change the oxidation potential of the metal centre. All the new compounds have been characterized in solution by 1 H, 11 B and 13 C NMR spectroscopy, mass spectrometry and the structural types of 3a–c and 4b were unequivocally established by crystallographic analysis. [ABSTRACT FROM AUTHOR]

The first example of a homometallic neutral zirconaborane, [(Cp2Zr)2B5H11], 1, has been prepared through the thermolysis of [Cp2Zr(BH4)2], generated from the fast metathesis reaction of [Cp2ZrCl2] and LiBH4·thf with BH3·thf. The solid-state structure of 1 shows an open geometry with a planar B3 ring. The bonding between the Zr center and the central B3 ring was studied computationally by DFT methods, and based on the combined experimental and computational results compound 1 can be defined as a metal-stabilized arachno-B3H9. Further, in an attempt to synthesize a hybrid analogue of 1 by introducing two electron fragments into arachno-[(Cp2Zr)(Cp*Ir)B4H10], 2, we have performed the reaction of 2 with [Ru3(CO)12]. However, the reaction led to the formation of a hybrid metallaborane, [(Cp*Ir){Ru3(CO)8}B4H10], 3. [ABSTRACT FROM AUTHOR]

Thermolysis of an in situ generated intermediate [(Cp*Ta)2(BH3)2Cl2], 1 generated from the reaction of [Cp*TaCl4], (Cp* = η5-C5Me5) and [LiBH4·thf], in presence of [Ru3(CO)12] yielded pileo-[Cp*TaCl(μ-Cl)-B2H4Ru3(CO)8], 2 having two electrons fewer than seven pairs required for the observed square pyramidal geometry. Cluster 2 is the first example of an unsaturated cluster comprising early and late transition metals in a square pyramid core. This reaction also yielded [(Cp*Ta)2(B2H6)(B2H4Cl2)], 3 as a by-product. In addition, the reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) with [LiBH4.thf] in presence of excess [MeI] at mild condition led to the isolation of periodinated dimolybdatetraborane [(Cp*Mo)2B4H3I5], 4 that hints a possible existence of [(Cp*Mo)2B4H8]. After the isolation of periodinated 4, we extended this chemistry towards the late transition metallaborane [(Cp*Rh)3B4H4], 5 using [PtBr2] as brominating source. Although all the attempts to isolate perbrominated rhodaborane failed, we have isolated partially brominated rhodaborane clusters [(Cp*Rh)3(BH)-(BBr)3], 6 and [(Cp*Rh)3(BH)3(BBr)], 7. All the compounds were characterized by IR and 1H, 11B and 13C NMR spectroscopy in solution, and the solid-state structures of 2, 4 and 6 were established by crystallographic analysis. [ABSTRACT FROM AUTHOR]

Thermolysis of an in situ generated intermediate [(Cp*Ta)2(BH3)2Cl2], 1 generated from the reaction of [Cp*TaCl4], (Cp* = η5-C5Me5) and [LiBH4·thf], in presence of [Ru3(CO)12] yielded pileo-[Cp*TaCl(μ-Cl)-B2H4Ru3(CO)8], 2 having two electrons fewer than seven pairs required for the observed square pyramidal geometry. Cluster 2 is the first example of an unsaturated cluster comprising early and late transition metals in a square pyramid core. This reaction also yielded [(Cp*Ta)2(B2H6)(B2H4Cl2)], 3 as a by-product. In addition, the reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) with [LiBH4.thf] in presence of excess [MeI] at mild condition led to the isolation of periodinated dimolybdatetraborane [(Cp*Mo)2B4H3I5], 4 that hints a possible existence of [(Cp*Mo)2B4H8]. After the isolation of periodinated 4, we extended this chemistry towards the late transition metallaborane [(Cp*Rh)3B4H4], 5 using [PtBr2] as brominating source. Although all the attempts to isolate perbrominated rhodaborane failed, we have isolated partially brominated rhodaborane clusters [(Cp*Rh)3(BH)-(BBr)3], 6 and [(Cp*Rh)3(BH)3(BBr)], 7. All the compounds were characterized by IR and 1H, 11B and 13C NMR spectroscopy in solution, and the solid-state structures of 2, 4 and 6 were established by crystallographic analysis. [ABSTRACT FROM AUTHOR]

Thermolysisof [(Cp*RuCO)2B2H6] (1; Cp* = η5-C5Me5) with [Ru3(CO)12] yielded the trimetallaborane[(Cp*RuCO)3(μ3-H)BH] (2)and a number of homometallic boride clusters: [Cp*RuCO{Ru(CO)3}4B] (3), [(Cp*Ru)2{Ru2(CO)8}BH] (4), and [(Cp*Ru)2{Ru4(CO)12}BH] (5). Compound 2is isoelectronic and isostructural with the triply bridgedborylene compounds [(μ3-BH)(Cp*RuCO)2(μ-CO){Fe(CO)3}] (6) and [(μ3-BH)(Cp*RuCO)2(μ-H)(μ-CO){Mn(CO)3}] (7), where the [μ3-BH] moiety occupies the apicalposition. To test if compound 2undergoes hydroborationreactions with alkynes, as observed with 6, we performedthe reaction of 2with the same set of alkynes underphotolytic conditions. However, neither 2nor 7undergoes hydroboration to yield a vinyl–borylene complex.On the other hand, thermolysis of 6with trimethylsilylethyleneyielded the novel diruthenacarborane [1,1,7,7,7-(CO)5-2,3-(Cp*)2-μ-2,3-(CO)-μ3-1,2,3-(CO)-5-(SiMe3)-pileo-1,7,2,3,4,5-Fe2Ru2C2BH] (8). The solid-state X-ray diffractionresults suggest that 8exhibits a pentagonal -bipyramidalgeometry with one additional CO capping one of its faces. Cluster 3is a boride cluster where boron is in the interstitial positionof a square-pyramidal geometry, whereas compound 4canbe described as a tetraruthenium boride in which the Ru4butterfly skeleton has an interstitial boron atom. Electronic structurecalculations of compound 2employing density functionaltheory (DFT) generate geometries in agreement with the structure determinations.The existence of a large HOMO–LUMO gap in 2isin agreement with its high stability. Bonding patterns in the structurehave been analyzed on the grounds of DFT calculations. Furthermore,the B3LYP-computed 11B and 1H chemical shiftsfor compound 2precisely follow the experimentally measuredvalues. All the compounds have been characterized by IR and 1H, 11B, and 13C NMR spectroscopy, and the geometriesof the structures were unambiguously established by crystallographicanalyses of 2–4and 8. [ABSTRACT FROM AUTHOR]

Abstract: The reactivity of two isoelectronic and isostructural metallaboranes, nido-[(Cp*Rh)2B6H10], 1 and nido-[(Cp*Ru)2B6H12], 2 with alkynes demonstrates that a change in metal from group 9 to group 8 creates difference in the reactivity pattern. Compound 1 catalyzes the cyclotrimerization of a variety of internal and terminal alkynes to yield 1,3,5- and 1,2,4-substituted benzene. In contrast, compound 2 shows no reactivity toward alkynes. A set of alkynes have been verified with nido-1 that yielded several benzene derivatives in satisfactory yields. [Copyright &y& Elsevier]

A comparative reactivity study of two isoelectronic nido ‐ dimetallapentaboranes with 2 ‐ mercaptobenzothiazole demonstrates the influence of metal change from Group 8 to Group 9. The former leads to the formation of B ‐ agostic, whereas the later affords a boratrane complex. In addition, the first example of a structurally characterized N,S ‐ heterocyclic carbene complex of rhodium is reported. For more details see the Full Paper by S. Ghosh et al. on page 3640 ff. [ABSTRACT FROM AUTHOR]