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.

No abstract