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.

Hydroboration of Alkynes: η4-Alkene-Borane versus η4-E-Boratabutadiene.

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.

Design, Synthesis, and Chemistry of Bis(σ)borate and Agostic Complexes of Group†7 Metals.

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[(H3 B)bbza]), trihydro(2-aminobenzothiazolyl)borate (Na[(H3 B)abz]), and dihydrobis(2-mercaptopyridyl)borate (Na[(H2 B)mp2 ]) (bbza=bis(benzothiazol-2-yl)amine, abz=2-aminobenzothiazolyl, and mp=2-mercaptopyridyl). Photolysis of [Mn2 (CO)10 ] with Na[(H3 B)bbza] formed bis(σ)borate complex [Mn(CO)3 (µ-H)2 BHNCSC6 H4 (NR)] (1; R=NCSC6 H4 ). Octahedral complex [Re(CO)2 (N3 C2 S2 C12 H8 )2 ] (2) was generated under similar reaction conditions with [Re2 (CO)10 ]. Similarly, when [Mn2 (CO)10 ] was treated with Na[(H3 B)abz], bis(σ)borate complex [Mn(CO)3 (µ-H)2 BH(HN2 CSC6 H4 )] (3) and the agostic complex [Mn(CO)3 (µ-H)BH(HN2 CSC6 H4 )2 ] (4) were formed. To probe the potential formation of agostic complexes of the heavier group 7 metals, we carried out the photolysis of [M2 (CO)10 ] with Na[(H2 B)mp2 ] and found that [M(CO)3 (µ-H)BH(C5 H4 NS)2 ] (5: M=Re; 6: M=Mn) was formed in moderate yield. Complexes 1 and 3 feature a (κ3 -H,H,N) coordination mode, whereas 4, 5, and 6 display both (κ3 -H,N,N) and (κ3 -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)2 (BHNCSC6 H4 )(NR)(CO)2 PL2 L'] (R=NCSC6 H4 ; 7 a: L=L'=Ph; 7 b: L=Ph, L'=Me) and [Mn(µ-H)2 BHN(NCSC6 H4 )R(CO)2 PL2 L'] (R=NCSC6 H4 ; 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.

An Efficient Method for the Synthesis of Boratrane Complexes of Late Transition Metals.

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)Clx ]2 as precursors (L'=η6 -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*=η5 -C5 Me5 ). For example, treatment of Na[(H3 B)bbza] or Na[(H2 B)mp2 ] (bbza=bis(benzothiazol-2-yl)amine; mp=2-mercaptopyridyl) with [L'M(µ-Cl)Clx ]2 yielded [(η6 -p-cymene)RuBH{(NCSC6 H4 )(NR)}2 ] (2; R=NCSC6 H4 ), [{N(NCSC6 H4 )2 }RhBH{(NCSC6 H4 )(NR)}2 ] (3; R=NCS-C6 H4 ), [(η6 -p-cymene)RuBH(L)2 ] (5; L=C5 H4 NS), and [Cp*MBH(L)2 ] (6 and 7; L=C5 H4 NS, M=Ir or Rh). In order to delineate the significance of the ligands, we studied the reactivity of [(COD)Rh(µ-Cl)]2 with Na[(H3 B)bbza], which led to the formation of the isomeric agostic complexes [(η4 -COD)Rh(µ-H)BHRh(C14 H8 N3 S2 )3 ], 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.

UV-C photon integrated surface dielectric barrier discharge hybrid reactor: A novel and energy-efficient route for rapid mineralisation of aqueous azo dyes.

The study describes developing an energy-efficient and scalable alternative to conventional non-thermal plasma systems by integrating surface dielectric barrier discharge (SDBD) and UV-C radiation sources. The unprecedented enhancement in the mineralisation rate of an azo dye (brilliant red 5B) by the hybrid reactor (photo-SDBD) is demonstrated thoroughly as a function of dye concentrations, pH, and background salts. The photo-SDBD is 1.25 - 4.9 times more energy efficient than SDBD under similar experimental conditions. The photo-SDBD could overcome the problems such as the recombination of hydroxyl radicals and scavenging of radicals by salts (NaCl, Na2SO4, Na2CO3) observed in conventional non-thermal plasma systems. The TOC and HR-MS analysis establish the complete mineralisation potential and chemical mineralisation pathway. Besides, the phytotoxicity of the treated water is tested and demonstrated its utility as a liquid fertiliser for enhanced germination of mung bean seeds. The optical emission spectroscopy measurements were performed to estimate the plasma's electron temperature (1.6 ± 0.2 eV) and density (1021/m3). The emission line ratio (I763.5/I738.3) approach is used to compare the influence of UV-C on plasma parameters in the SDBD reactor. The study opens a new pathway for developing energy-efficient and scalable plasma-assisted mineralisation of complex and emerging organic pollutants.

Heterometallic Triply-Bridging Bis-Borylene Complexes.

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*=η5 -C5 Me5 ) and [LiBH4 ⋅THF] afforded triply-bridging bis-{hydrido(borylene)}, [(µ3 -BH)2 H2 {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 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 [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 (B3 H7 )], which afforded triply-bridging bis-borylene species [(µ3 -BH)2 (RhCp*)2 Co2 (CO)4 (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.