A series of new bis(σ)borate and agostic complexes of group 7 metals have been synthesized and structurally characterized from various borate ligands, such as trihydrobis(benzothiazol-2-yl)amideborate (Na[(H B)bbza]), trihydro(2-aminobenzothiazolyl)borate (Na[(H B)abz]), and dihydrobis(2-mercaptopyridyl)borate (Na[(H B)mp ]) (bbza=bis(benzothiazol-2-yl)amine, abz=2-aminobenzothiazolyl, and mp=2-mercaptopyridyl). Photolysis of [Mn (CO) ] with Na[(H B)bbza] formed bis(σ)borate complex [Mn(CO) (μ-H) BHNCSC H (NR)] (1; R=NCSC H ). Octahedral complex [Re(CO) (N C S C H ) ] (2) was generated under similar reaction conditions with [Re (CO) ]. Similarly, when [Mn (CO) ] was treated with Na[(H B)abz], bis(σ)borate complex [Mn(CO) (μ-H) BH(HN CSC H )] (3) and the agostic complex [Mn(CO) (μ-H)BH(HN CSC H ) ] (4) were formed. To probe the potential formation of agostic complexes of the heavier group 7 metals, we carried out the photolysis of [M (CO) ] with Na[(H B)mp ] and found that [M(CO) (μ-H)BH(C H NS) ] (5: M=Re; 6: M=Mn) was formed in moderate yield. Complexes 1 and 3 feature a (κ -H,H,N) coordination mode, whereas 4, 5, and 6 display both (κ -H,N,N) and (κ -H,S,S) modes of the corresponding ligands. To investigate the lability of the CO ligands of 1 and 3, we treated the complexes with phosphine ligands that generated novel bis(σ)borate complexes [Mn(μ-H) (BHNCSC H )(NR)(CO) PL L'] (R=NCSC H ; 7 a: L=L'=Ph; 7 b: L=Ph, L'=Me) and [Mn(μ-H) BHN(NCSC H )R(CO) PL L'] (R=NCSC H ; 8 a: L=L'=Ph; 8 b: L=Ph, L'=Me). Complexes 7 and 8 are structural isomers with different coordination modes of the bbza ligand. In addition, DFT calculations were performed to shed some light on the bonding and electronic structures of these complexes.

A series of hydroborated η4-σ,π-alkene–borane complexes have been synthesized from the reaction of ruthenium–bis­(σ)­borate complex [Cp*Ru­(μ-H)2BH­(S-CHS)] (1) and terminal as well as internal alkynes. Likewise, the reactions of manganese–bis­(σ)­borate complexes [Mn­(CO)3(μ-H)2BHNCSC6H4(NL)] (L = NCSC6H4 or H) were explored with terminal alkynes that yielded boratabutadiene complexes [Mn­(CO)3{(NCSC6H4)2N}­{(R1MeC)B­(HCCHR1)}] [R1 = phenyl (4a) or p-tolyl (4b)] via triple hydroboration of alkynes. These complexes feature a boratabutadiene ligand that is coordinated to a metal through the η4-CBCC mode. To the best of our knowledge, these are the first examples of η4-E-boratabutadiene-coordinated manganese complexes generated by the trans-hydroboration of alkynes. The steric and electronic effects of the borate ligands have been demonstrated using a less sterically hindered manganese–bis­(σ)­borate complex, [Mn­(CO)3(μ-H)2BH­(HN2CSC6H4)], that generated monohydroborated complexes [(CO)3Mn­(μ-H)2(HN2CSC6H4)­B­(R1CCHR2)] (for 6, R1 = Ph and R2 = H; for 7, R1 = p-Tol and R2 = H; for 8, R1 = R2 = Ph). Theoretical studies using density functional theory methods and chemical bonding analyses established the bonding and stability of these species.

In a quest for efficient precursors for the synthesis of boratrane complexes of late transition metals, we have developed a useful synthetic method using [L'M(μ-Cl)Cl ] as precursors (L'=η -p-cymene, M=Ru, x=1; L'=COD, M=Rh, x=0 and L'=Cp*, M=Ir or Rh, x=1; COD=1,5-cyclooctadiene, Cp*=η -C Me ). For example, treatment of Na[(H B)bbza] or Na[(H B)mp ] (bbza=bis(benzothiazol-2-yl)amine; mp=2-mercaptopyridyl) with [L'M(μ-Cl)Cl ] yielded [(η -p-cymene)RuBH{(NCSC H )(NR)} ] (2; R=NCSC H ), [{N(NCSC H ) }RhBH{(NCSC H )(NR)} ] (3; R=NCS-C H ), [(η -p-cymene)RuBH(L) ] (5; L=C H NS), and [Cp*MBH(L) ] (6 and 7; L=C H NS, M=Ir or Rh). In order to delineate the significance of the ligands, we studied the reactivity of [(COD)Rh(μ-Cl)] with Na[(H B)bbza], which led to the formation of the isomeric agostic complexes [(η -COD)Rh(μ-H)BHRh(C H N S ) ], 4 a and 4 b, in parallel to the formation of 16-electron square-pyramidal rhodaboratrane complex 3. Compounds 4 a and 4 b show two different geometries, in which the Rh-B bonds are shorter than in the reported Rh agostic complexes. The new compounds have been characterized in solution by various spectroscopic analyses, and their structural arrangements have been unequivocally established by crystallographic analyses. DFT calculations provide useful insights regarding the stability of these metallaboratrane complexes as well as their M→B bonding interactions.

Triply bridging bis-{hydrido(borylene)} and bis-borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe2(CO)9] with an in situ produced intermediate, generated from the low temperature reaction of [Cp*WCl4] (Cp* = η 5-C5Me5) and [LiBH4•THF] afforded triply-bridging bis-{hydrido (borylene)}, [(µ3-BH)2H2{Cp*W(CO)2}2{Fe(CO)2}] (1) and bis-borylene, [(µ3-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 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 [Ru3(CO)12]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(µ3-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 [Co2(CO)8] with nido-[(RhCp*)2(B3H7)], which afforded triply-bridging bis-borylene species [(µ3-BH)2(RhCp*)2Co2(CO)5(µ-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; 1 H, 11 B, 13 C NMR spectroscopy; IR spectroscopy and mass spectrometry.

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The complexes [Ag{κ 3 -S,SЈ,H-H 2 B(mbz) 2 }(PR 3 )] x , (1: x = 2, R = Ph; 2: x = 1, R = Cy) (mbz = 2-mercaptobenzothiazolyl) and amidine based dihydro(2-mercaptobenzo-thiazolyl) borates, [HN=C(Ph)-NH(R)-H 2 B(mbz)] (3: R = 2,6-diisopropylphenyl and 4: R = Ph) were synthesized and characterized by various spectroscopic methods and single-crystal X-ray crystallography. Complex [Ag{κ 3 -S,SЈ,H-H 2 B(mbz) 2 }(PPh 3 )] 2 (1) has a dimeric structure in its crystalline state, in which central silver(I) atoms adopt a * Prof. Dr. S. Ghosh E-Mail: sghosh@iitm.ac.in [a] 588 distorted trigonal bipyramid arrangement. In contrast, complex [Ag{κ 3 -S,SЈ,H-H 2 B(mbz) 2 }(PCy 3 )] (2) has a monomeric structure in its crystalline state, in which the central silver(I) atoms adopt a distorted trigonal planar arrangement. Infrared spectroscopy was utilized as a tool for investigating the presence of M···H-B interactions. In addition, density functional theory (DFT) calculations were used to analyse the B-H···[M] bonding interaction in the metal borate complexes. Crystal Data for 1: C 64 H 50 B 2 Ag 2 S 8 N 4 P 2 , M r = 1430.86, triclinic, P1, a = 11.5839(8) Å, b = 11.6836(8) Å, c = 12.2097(9) Å, α = 76.233(6)°, β = 80.921(6)°, γ = 73.582(6)°, V = 1532.3(2) Å 3 , Z = 1, ρ calcd. = 1.551 mg·m -3 , μ = 1.009 mm -1 , F(000) = 724, R 1 = 0.0507, wR 2 = 0.0653, 7252 independent reflections [2θ Յ 58.48°] and 378 parameters, Goodness-of-fit on F 2 = 1.029. Crystal Data for 2: C 32 H 43 BAgS 4 N 2 P, M r = 733.57, monoclinic, P2 1 /n, a = 9.7847(3) Å, b = 25.6692(6) Å, c = 13.9303(4) Å, α = 90°, β = 99.334(3)°, γ = 90°, V = 3452.48(17) Å 3 , Z = 4, ρ calcd. = 1.411 mg·m -3 , μ = 0.897 mm -1 , F(000) = 1520, R 1 = 0.0574, wR 2 = 0.0979, 8391 independent reflections [2θ Յ 58.066°] and 378 parameters, Goodness-of-fit on F 2 = 1.034. Crystal Data for 3: C 26 H 30 BS 2 N 3 , M r = 457.44, monoclinic, P2 1 /n, a = 12.8305(5) Å, b = 14.3085(4) Å, c = 13.9844(4) Å, α = 90°, β = 98.940(3)°, γ = 90°, V = 2536.14(14) Å 3 , Z = 4, ρ calcd. = 1.198 mg·m -3 , μ = 0.228 mm -1 , F(000) = 968, R 1 = 0.1074, wR 2 = 0.1880, 8484 independent reflections [2θ Յ 64.764°] and 310 parameters, Goodness-of-fit on F 2 = 1.106. Crystal Data for 4: C 20 H 18 BS 2 N 3 , M r = 585.61, monoclinic, P2 1 /c, a = 9.9343(10) Å, b = 14.2927(17) Å, c = 23.194(3) Å, α = 90°, β = 92.483(4)°, γ = 90°, V = 3290.2(6) Å 3 , Z = 4, ρ calcd. = 1.182 mg·m -3 , μ = 0.192 mm -593 independent reflections [2θ Յ 50.998°] and 447 parameters, Goodness-of-fit on F 2 = 1.032.Supporting Information (see footnote on the first page of this article): Detailed information about the packing diagram of compounds 3 and 4, spectroscopic data and DFT-computed results for compounds 1, 2, 3 and 4 have been provided in the supporting information.

A series of metal-rich metallaboranes of groups 7 and 9 comprising triply bridging borylene and boride units have been isolated and structurally characterized. Thermolysis of nido-[(RhCp*) 2 B 3 H 7 ] (1; Cp* = η 5 -C 5 Me 5 ) with [Co 2 (CO) 8 ] led to the isolation of tetrametallic [(μ 3 -BH)(RhCp*) 2 (μ-CO)(μ 3 -CO){Co 2 (CO) 4 }] (2), featuring a triply bridging borylene unit, and the trimetallic cluster [(μ 3 -BH)(μ-H)(RhCp*) 2 (μ-CO) 3 {Co(CO)}] (3) that contains a triply bridging hydrido(borylene) unit. The borylene {BH} unit of 2 is coordinated to a deltahedral face of a tetrametallic tetrahedron in a μ 3 fashion. Cluster 3 is a rare example of a tetrahedral metallaborane featuring a hydrido(borylene) unit. In an attempt to synthesize the Mn analogues of 2 and 3, a similar reaction was carried out with [Mn 2 (CO) 10 ] that afforded the trimetallic cluster [(μ 3 -BH)(RhCp*) 2 (μ-CO) 3 {MnH(CO) 3 }] (5) having a triply bridging borylene moiety, the two heterometallic μ 9 -boride clusters [(RhCp*) 3 {Rh(CO)} 3 (μ-CO) 3 {MnH(CO) 3 }B 3 H 2 ] (6) and [(RhCp*) 3 {Mn-(CO) 3 } 2 Rh(CO) 2 B 4 H 3 ] ( 7) and the unusual tetrametallic complex [(RhCp*) 2 (μ-CO) 2 (μ 3 -η 3 -CO 2 ){Mn 2 (CO) 9 }] (8). Clusters 6 and 7 are both unusual heterometallic metal-rich boride clusters, where the boride boron atom is encapsulated inside a tricapped trigonal prism depicting a μ 9 -bonding mode. Compound 8 is a unique example of a metal carbonyl compound in which a CO 2 group is bridging two Rh atoms and one Mn atom in a μ 3 -η 3 fashion. To explore this chemistry with a heavier transition metal, we have carried out the thermolysis of arachno-[IrCp*H 2 (B 3 H 7 )] ( 9) with [Mn 2 (CO) 10 ], which afforded the face-fused iridaborane cluster [(IrCp*) 3 {Ir(CO) 2 } 3 (μ-CO)(μ 3 -CO)B] (10). Compound 10 can also be viewed as a boride cluster, where the naked boron is coordinated to iridium centers in a unique μ 5 coordination mode. All of the compounds have been characterized by 1 H, 11 B, and 13 C NMR spectroscopy and mass spectrometry, and the structures of 2, 3, 5, 6, 8, and 10 have been unambiguously established by crystallographic analyses. Computational studies show that a substantial amount of overlap occurs between the metal frameworks and borylene/boride units.

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