Cooperative B-H bond activation: dual site borane activation by redox active κ2-N,S-chelated complexes.

Cooperative dual site activation of boranes by redox-active 1,3-N,S-chelated ruthenium species, mer-[PR3{κ2-N,S-(L)}2Ru{κ1-S-(L)}], (mer-2a: R = Cy, mer-2b: R = Ph; L = NC7H4S2), generated from the aerial oxidation of borate complexes, [PR3{κ2-N,S-(L)}Ru{κ3-H,S,S'-BH2(L)2}] (trans-mer-1a: R = Cy, trans-mer-1b: R = Ph; L = NC7H4S2), has been investigated. Utilizing the rich electronic behaviour of these 1,3-N,S-chelated ruthenium species, we have established that a combination of redox-active ligands and metal-ligand cooperativity has a big influence on the multisite borane activation. For example, treatment of mer-2a-b with BH3·THF led to the isolation of fac-[PR3Ru{κ3-H,S,S'-(NH2BSBH2N)(S2C7H4)2}] (fac-3a: R = Cy and fac-3b: R = Ph) that captured boranes at both sites of the κ2-N,S-chelated ruthenacycles. The core structure of fac-3a and fac-3b consists of two five-membered ruthenacycles [RuBNCS] which are fused by one butterfly moiety [RuB2S]. Analogous fac-3c, [PPh3Ru{κ3-H,S,S'-(NH2BSBH2N)(SC5H4)2}], can also be synthesized from the reaction of BH3·THF with [PPh3{κ2-N,S-(SNC5H4)}{κ3-H,S,S'-BH2(SNH4C5)2}Ru], cis-fac-1c. In stark contrast, when mer-2b was treated with BH2Mes (Mes = 2,4,6-trimethyl phenyl) it led to the formation of trans- and cis-bis(dihydroborate) complexes [{κ3-S,H,H-(NH2BMes)Ru(S2C7H4)}2], (trans-4 and cis-4). Both the complexes have two five-membered [Ru-(H)2-B-NCS] ruthenacycles with κ2-H-H coordination modes. Density functional theory (DFT) calculations suggest that the activation of boranes across the dual Ru-N site is more facile than the Ru-S one.

Cooperative B-H and Si-H Bond Activations by κ2-N,S-Chelated Ruthenium Borate Complexes.

Cooperative E-H (E = B, Si) bond activations employing κ2-N,S-chelated ruthenium borate species, [PPh3{κ2-N,S-(NS2C7H4)}Ru{κ3-H,S,S'-H2B(NC7H4S2)2}], (1) are established. Treatment of 1 with BH3·SMe2 yielded the six-membered ruthenaheterocycle [PPh3{κ2-S,H-(BH3NS2C7H4)}Ru{κ3-H,S,S'-H2B(C7H4NS2)2}] (2) formed by a hemilabile ring opening of a Ru-N bond and capturing of a BH3 unit coordinated in an "end-on" fashion. On the other hand, the bulky borane H2BMes shows different reactivity with 1 that led to the formation of the two dihydroborate complexes [{κ3-S,H,H-(NBH2Mes)(S2C7H4)}Ru{κ3-H,S,S'-H2B(C7H4NS2)2}] (3) and [PPh3{κ3-S,H,H-(NBH2Mes)(S2C7H4)}Ru(κ2-N,S-C7H4NS2)] (4), in which H2BMes has been inserted into the Ru-N bond of the initial κ2-N,S-chelated ligand. In an attempt to directly activate hydrosilanes by 1, reactions were carried out with H2SiPh2 that yielded two isomeric five-membered ruthenium silyl complexes, namely [PPh3{κ2-S,Si-(NSiPh2)(S2C7H4)}Ru{κ3-H,S,S'-H2B(C7H4NS2)2}] (5a,b), and the hydridotrisilyl complex [Ru(H){κ2-S,Si-(SiPh2NC7H4S2}3] (6). These complexes were generated by Si-H bond activation with the release of H2 and the formation of N-Si and Ru-Si bonds. When the reaction of 1 was carried out in the presence of PhSiH3, the reaction only produced the analogous complexes [PPh3{κ2-S,Si-(NSiPhH)(S2C7H4)}Ru{κ3-H,S,S'-H2B(C7H4NS2)2}] (5a',b'). Density functional theory (DFT) calculations have been used to probe the bonding modes of boranes/silane with the ruthenium center.

A BN-Doped Cycloparaphenylene Debuts.

The first example of a BN-doped cycloparaphenylene BN-[10]CPP was synthesized and characterized. Its reactivity and photophysical properties were evaluated in direct comparison to its carbonaceous analogues Mes-[10]CPP and [10]CPP. While the photophysical properties of BN-[10]CPP remains similar to its carbonaceous analogues, the electronic structure changes associated with the introduction of a 1,2-azaborine BN heterocycle into a CPP scaffold enables facile and selective late-stage functionalizations that cannot be accomplished with carbonaceous CPPs. Specifically, Ir-catalyzed hydrogenation of BN-[10]CPP selectively reduces the BN heterocyclic ring, which upon hydrolysis produces a rare example of a macrocyclic paraphenylene 6 incorporating the versatile ketone functionality within the macrocyclic ring.

Homocubane Chemistry: Synthesis and Structures of Mono- and Dicobaltaheteroborane Analogues of Tris- and Tetrahomocubanes.

Room-temperature reactions between [Cp*CoCl]2 (Cp* = η5-C5Me5) and large excess of [BH2E3]Li (E = S or Se) led to the formation of homocubane derivatives, 1-7. These species are bimetallic tetrahomocubane, [(Cp*Co)2(µ-S)4(µ3-S)4B2H2], 1; bimetallic trishomocubane isomers, [(Cp*Co)2(µ-S)3(µ3-S)4B2H2], 2 and 3; monometallic trishomocubanes, [M(µ-E)3(µ3-E)4B3H3] [4: M = Cp*Co, E = S; 5: M = Cp*Co, E = Se and 6: M = {(Cp*Co)2(µ-H)(µ3-Se)2}Co, E = Se], and bimetallic homocubane, [(Cp*Co)2(µ-Se)(µ3-Se)4B2H2], 7. As per our knowledge, 1 is the first isolated and structurally characterized parent prototype of the 1,2,2',4 isomer of tetrahomocubane, while 3, 4, and 5 are the analogues of parent D 3-trishomocubane. Compounds 2 and 3 are the structural isomers in which the positions of the µ-S ligands in the trishomocubane framework are altered. Compound 6 is an example of a unique vertex-fused trishomocubane derivative, in which the D 3-trishomocubane [Co(µ-Se)3(µ3-Se)4B3H3] moiety is fused with an exopolyhedral trigonal bipyramid (tbp) moiety [(Cp*Co)2(µ-H)(µ3-Se)2}Co]. Multinuclear NMR and infrared spectroscopy, mass spectrometry, and single crystal X-ray diffraction analyses were employed to characterize all the compounds in solution. Bonding in these homocubane analogues has been elucidated computationally by density functional theory methods.

Five-Membered Ruthenacycles: Ligand-Assisted Alkyne Insertion into 1,3-N,S-Chelated Ruthenium Borate Species.

Building upon previous work, the chemistry of [(η6 -p-cymene)Ru{P(OMe)2 OR}Cl2 ], (R=H or Me) has been extended with [H2 B(mbz)2 ]- (mbz=2-mercaptobenzothiazolyl) using different Ru precursors and borate ligands. As a result, a series of 1,3-N,S-chelated ruthenium borate complexes, for example, [(κ2 -N,S-L)PR3 Ru{κ3 -H,S,S'-H2 B(L)2 }], (2 a-d and 2 a'-d'; R=Ph, Cy, OMe or OPh and L=C5 H4 NS or C7 H4 NS2 ) and [Ru{κ3 -H,S,S'-H2 B(L)2 }2 ], (3: L=C5 H4 NS, 3': L=C7 H4 NS2 ) were isolated upon treatment of [(η6 -p-cymene)RuCl2 PR3 ], 1 a-d (R=Ph, Cy, OMe or OPh) with [H2 B(mp)2 ]- or [H2 B(mbz)2 ]- ligands (mp=2-mercaptopyridyl). All the Ru borate complexes, 2 a-d and 2 a'-d' are stabilized by phosphine/phosphite and hemilabile N,S-chelating ligands. Treatment of these Ru borate species, 2 a'-c' with various terminal alkynes yielded two different types of five-membered ruthenacycle species, namely [PR3 {C7 H4 S2 -(E)-N-C=CH(R')}Ru{κ3 -H,S,S'-H2 B(L)2 }], (4-4'; R=Ph and R'=CO2 Me or C6 H4 NO2 ; L=C7 H4 NS2 ) and [PR3 {C7 H4 NS-(E)-S-C=CH(R')}Ru{κ3 -H,S,S'-H2 B(L)2 }], (5-5', 6 and 7; R=Ph, Cy or OMe and R'=CO2 Me or C6 H4 NO2 ; L=C7 H4 NS2 ). All these five-membered ruthenacycle species contain an exocyclic C=C moiety, presumably formed by the insertion of a terminal alkyne into the Ru-N and Ru-S bonds. The new species have been characterized spectroscopically and the structures were further confirmed by single-crystal X-ray diffraction analysis. Theoretical studies and chemical-bonding analyses established that charge transfer occurs from phosphorus to ruthenium center following the trend PCy3

Correction: Mercapto-benzothiazolyl based ruthenium(ii) borate complexes: synthesis and reactivity towards various phosphines.

Correction for 'Mercapto-benzothiazolyl based ruthenium(ii) borate complexes: synthesis and reactivity towards various phosphines' by Mohammad Zafar, et al., Dalton Trans., 2019, DOI: 10.1039/c9dt00498j.

Mercapto-benzothiazolyl based ruthenium(ii) borate complexes: synthesis and reactivity towards various phosphines.

The synthesis and reactivity of ruthenium complexes containing an anionic boron based ligand, supported by mercapto-benzothiazolyl heterocycles are presented. Specifically, the reaction of [(η6-p-cymene)Ru{P(OMe)2OR}Cl2], (1a: R = Me; 1b: R = H) with [H2B(mbz)2]- (mbz = 2-mercaptobenzothiazolyl) at room temperature afforded a series of borate complexes, namely [(L)Ru{κ3-H,S,S'-H2B(L)2}P(O)(OMe)(HL)], 2, [Ru{κ3-H,S,S'-H2B(L)2}2], 3 and [(κ2-N,S-L)P(OMe)3Ru{κ3-H,S,S'-H2B(L)2}], 4a; (L = C7H4NS2). The pivotal feature of 2 is the coordination of the Ru centre with a phosphorus atom of secondary phosphine oxide and mercapto-benzothiazolyl ligands. On the other hand, 3 features dual RuH-B interactions between Ru and B-H bonds of [H2B(mbz)2]-. Interestingly, along with 3, compound [(κ2-N,S-L)P(OPh)3Ru{κ3-H,S,S'-H2B(L)2}], 4b (L = C7H4NS2), was isolated upon treatment of the same borate with [(η6-p-cymene)RuCl2P(OPh)3], 1c, which is stabilized by δ-B-H interactions and one phosphite ligand. Furthermore, compound 3 promptly reacts with P(OR)3 to generate [(OR)3PRu-{κ2-S,S'-H2B(L)2}{κ3-H,S,S'-H2B(L)2}], (5a: R = Me, 5b: R = Ph; L = C7H4NS2) by breaking one of the RuH-B interactions. Upon heating, compound 5a converts into [(OMe)2OPRu{κ2-S,S'-HB(L)2}{κ3-H,S,S'-H2B(L)2}], 6a (L = C7H4NS2) by release of methane gas. Compound 6a is a unique example wherein the boron atom of the borate ligand is bound to an oxygen atom of the phosphite unit. In contrast, the thermolysis of 3 with PR2R' yielded [Ru{κ3-H,S,S'-H2B(L2)}(PR2R')2(L)], (7a: R = Me, R' = Ph; 7b: R = Ph; R' = Me; L = C7H4NS2), respectively, revealing the incorporation of two triphosphine ligands in the coordination sphere of ruthenium. Density functional theory (DFT) calculations were undertaken to provide an insight into the electronic structures of the complexes.

Cluster Fusion: Face-Fused Macropolyhedral Tetracobaltaboranes.

In an effort to isolate the 16-vertex supraicosahedral cobaltaborane [(Cp*Co)3B12H12Co{Cp*CoB4H9}] (Cp* = η5-C5Me5), we have pyrolyzed an in situ generated intermediate, obtained from the fast metathesis of [Cp*CoCl]2 and [LiBH4·THF], with an excess amount of [BH3·THF]. Although the objective of isolating the 16-vertex cobalt analogue was not achieved, the reaction yielded a closo-19-vertex face-fused cluster presenting icosahedral {Co3B9}, tetrahedral {B4}, and 10-vertex {CoB9} units. The reaction also yielded a 20-vertex face-fused cluster that contains icosahedral {Co4B8}, square-pyramidal {CoB4}, tetrahedral {Co2B2}, and nido-{CoB7} units.

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.

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.

Reactivity of cyclopentadienyl transition metal(ii) complexes with borate ligands: structural characterization of the toluene-activated molybdenum complex [Cp*Mo(CO)2(η3-CH2C6H5)].

Reactions of cyclopentadienyl transition-metal halide complexes [Cp*Mo(CO)3Cl], 1, and [CpFe(CO)2I], 2, (Cp = C5H5; Cp* = η5-C5Me5) with borate ligands are reported. Treatment of 1 with [NaBt2] (Bt2 = dihydrobis(2-mercapto-benzothiazolyl)borate) in toluene yielded [Cp*Mo(CO)2(C7H4S2N)], 3, and [Cp*Mo(CO)2(η3-CH2C6H5)], 4, with a selective binding of toluene through C-H activation followed by orthometallation. Note that compound 4 is a structurally characterized toluene-activated molecule in which the metal is in η3-coordination mode. Under similar reaction conditions, [NaPy2] (Py2 = dihydrobis(2-mercaptopyridyl)borate) produced only the mercaptopyridyl molybdenum complex [Cp*Mo(CO)2(C5H4SN)], 5, in good yield. On the other hand, when compound 2 was treated individually with [NaBt] (Bt = trihydro(2-mercapto-benzothiazolyl)borate) and [NaPy2] in THF, formation of the η1-coordinated complexes [CpFe(CO)2(C7H4S2N)], 6, and [CpFe(CO)2(C5H4SN)], 7, was observed. The solid-state molecular structures of compounds 3, 4, 6, and 7 have been established by single-crystal X-ray crystallographic analyses.

η(4) -HBCC-σ,π-Borataallyl Complexes of Ruthenium Comprising an Agostic Interaction.

Thermolysis of [Cp*Ru(PPh2 (CH2 )PPh2 )BH2 (L2 )] 1 (Cp*=η(5) -C5 Me5 ; L=C7 H4 NS2 ), with terminal alkynes led to the formation of η(4) -σ,π-borataallyl complexes [Cp*Ru(µ-H)B{R-C=CH2 }(L)2 ] (2 a-c) and η(2) -vinylborane complexes [Cp*Ru(R-C=CH2 )BH(L)2 ] (3 a-c) (2 a, 3 a: R=Ph; 2 b, 3 b: R=COOCH3 ; 2 c, 3 c: R=p-CH3 -C6 H4 ; L=C7 H4 NS2 ) through hydroboration reaction. Ruthenium and the HBCC unit of the vinylborane moiety in 2 a-c are linked by a unique η(4) -interaction. Conversions of 1 into 3 a-c proceed through the formation of intermediates 2 a-c. Furthermore, in an attempt to expand the library of these novel complexes, chemistry of σ-borane complex [Cp*RuCO(µ-H)BH2 L] 4 (L=C7 H4 NS2 ) was investigated with both internal and terminal alkynes. Interestingly, under photolytic conditions, 4 reacts with methyl propiolate to generate the η(4) -σ,π-borataallyl complexes [Cp*Ru(µ-H)BH{R-C=CH2 }(L)] 5 and [Cp*Ru(µ-H)BH{HC=CH-R}(L)] 6 (R=COOCH3 ; L=C7 H4 NS2 ) by Markovnikov and anti-Markovnikov hydroboration. In an extension, photolysis of 4 in the presence of dimethyl acetylenedicarboxylate yielded η(4) -σ,π-borataallyl complex [Cp*Ru(µ-H)BH{R-C=CH-R}(L)] 7 (R=COOCH3 ; L=C7 H4 NS2 ). An agostic interaction was also found to be present in 2 a-c and 5-7, which is rare among the borataallyl complexes. All the new compounds have been characterized in solution by IR, (1) H, (11) B, (13) C NMR spectroscopy, mass spectrometry and the structural types were unequivocally established by crystallographic analysis of 2 b, 3 a-c and 5-7. DFT calculations were performed to evaluate possible bonding and electronic structures of the new compounds.

New Routes to a Series of σ-Borane/Borate Complexes of Molybdenum and Ruthenium.

A series of agostic σ-borane/borate complexes have been synthesized and structurally characterized from simple borane adducts. A room-temperature reaction of [Cp*Mo(CO)3 Me], 1 with Li[BH3 (EPh)] (Cp*=pentamethylcyclopentadienyl, E=S, Se, Te) yielded hydroborate complexes [Cp*Mo(CO)2 (µ-H)BH2 EPh] in good yields. With 2-mercapto-benzothiazole, an N,S-carbene-anchored σ-borate complex [Cp*Mo(CO)2 BH3 (1-benzothiazol-2-ylidene)] (5) was isolated. Further, a transmetalation of the B-agostic ruthenium complex [Cp*Ru(µ-H)BHL2 ] (6, L=C7 H4 NS2 ) with [Mn2 (CO)10 ] affords a new B-agostic complex, [Mn(CO)3 (µ-H)BHL2 ] (7) with the same structural motif in which the central metal is replaced by an isolobal and isoelectronic [Mn(CO)3 ] unit. Natural-bond-orbital analyses of 5-7 indicate significant delocalization of the electron density from the filled σBH orbital to the vacant metal orbital.

First-row transition-metal-diborane and -borylene complexes.

A combined experimental and quantum chemical study of Group 7 borane, trimetallic triply bridged borylene and boride complexes has been undertaken. Treatment of [{Cp*CoCl}2 ] (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) with LiBH4 ⋅thf at -78 °C, followed by room-temperature reaction with three equivalents of [Mn2 (CO)10 ] yielded a manganese hexahydridodiborate compound [{(OC)4 Mn}(η(6) -B2 H6 ){Mn(CO)3 }2 (µ-H)] (1) and a triply bridged borylene complex [(µ3 -BH)(Cp*Co)2 (µ-CO)(µ-H)2 MnH(CO)3 ] (2). In a similar fashion, [Re2 (CO)10 ] generated [(µ3 -BH)(Cp*Co)2 (µ-CO)(µ-H)2 ReH(CO)3 ] (3) and [(µ3 -BH)(Cp*Co)2 (µ-CO)2 (µ-H)Co(CO)3 ] (4) in modest yields. In contrast, [Ru3 (CO)12 ] under similar reaction conditions yielded a heterometallic semi-interstitial boride cluster [(Cp*Co)(µ-H)3 Ru3 (CO)9 B] (5). The solid-state X-ray structure of compound 1 shows a significantly shorter boron-boron bond length. The detailed spectroscopic data of 1 and the unusual structural and bonding features have been described. All the complexes have been characterized by using (1) H, (11) B, (13) C NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis. The DFT computations were used to shed light on the bonding and electronic structures of these new compounds. The study reveals a dominant B-H-Mn, a weak B-B-Mn interaction, and an enhanced B-B bonding in 1.

Synthesis, characterization and crystal structure analysis of cobaltaborane and cobaltaheteroborane clusters.

Cluster expansion reactions of cobaltaboranes were carried out using mono metal-carbonyls, metal halides and dichalcogenide ligands. Thermolysis of an in situ generated intermediate, obtained from the reaction of [Cp*CoCl]2 (Cp* = C5Me5) and [LiBH4·thf], with three equivalents of [Mo(CO)3(CH3CN)3] followed by the reaction with methyl iodide yielded isocloso-[(Cp*Co)3B6H7Co(CO)2] (1) and closo-[(Cp*Co)2B2H5Mo2(CO)6I] (2). Cluster 1 is ascribed to the isocloso structure based on a 10-vertex bicapped square antiprism geometry. In a similar manner, the reaction of [Cp*CoCl]2 with [LiBH4·thf] and the dichalcogenide ligand RS-SR (R = 1-OH-2,6-((t)Bu)2-C6H2) yielded nido cluster [(Cp*Co)2B2H2S2] (3). In parallel with the formation of the compounds 1-3, these reactions also yielded known cobaltaboranes [(Cp*Co)2B4H6] (4) and [(Cp*Co)3B4H4] in good yields. After the isolation of compound 4 in good yield, we verified its reactivity with PtBr2, which yielded closo-[(Cp*Co)2B4H2Br4] (5). To the best of our knowledge this is the second perhalogenated metallaborane cluster which has been recognized. All the new compounds were characterized by elemental analysis, IR, (1)H, (11)B, and (13)C NMR spectroscopy, and the geometric structures were unequivocally established by the X-ray diffraction analysis of compounds 1, 2, 3 and 5. Geometries obtained from the electronic structure calculations employing density functional theory (DFT) are in close agreement with the solid state X-ray structures. In addition, we analyzed the variation in the stability of the model compounds 1' (1': Cp analogue of 1, Cp = C5H5), [(CpCo)4B6H6] (1a) and [(CpRh)4B6H6] (1b).

New heteronuclear bridged borylene complexes that were derived from [{Cp*CoCl}2] and mono-metal-carbonyl fragments.

The synthesis, structural characterization, and reactivity of new bridged borylene complexes are reported. The reaction of [{Cp*CoCl}2] with LiBH4·THF at -70 °C, followed by treatment with [M(CO)3(MeCN)3] (M=W, Mo, and Cr) under mild conditions, yielded heteronuclear triply bridged borylene complexes, [(µ3-BH)(Cp*Co)2(µ-CO)M(CO)5] (1-3; 1: M=W, 2: M=Mo, 3: M=Cr). During the syntheses of complexes 1-3, capped-octahedral cluster [(Cp*Co)2(µ-H)(BH)4{Co(CO)2}] (4) was also isolated in good yield. Complexes 1-3 are isoelectronic and isostructural to [(µ3-BH)(Cp*RuCO)2(µ-CO){Fe(CO)3}] (5) and [(µ3-BH)(Cp*RuCO)2(µ-H)(µ-CO){Mn(CO)3}] (6), with a trigonal-pyramidal geometry in which the µ3-BH ligand occupies the apical vertex. To test the reactivity of these borylene complexes towards bis-phosphine ligands, the room-temperature photolysis of complexes 1-3, 5, 6, and [{(µ3-BH)(Cp*Ru)Fe(CO)3}2(µ-CO)] (7) was carried out. Most of these complexes led to decomposition, although photolysis of complex 7 with [Ph2P(CH2)(n)PPh2] (n=1-3) yielded complexes 9-11, [3,4-(Ph2P(CH2)(n)PPh2)-closo-1,2,3,4-Ru2Fe2(BH)2] (9: n=1, 10: n=2, 11: n=3). Quantum-chemical calculations by using DFT methods were carried out on compounds 1-3 and 9-11 and showed reasonable agreement with the experimentally obtained structural parameters, that is, large HOMO-LUMO gaps, in accordance with the high stabilities of these complexes, and NMR chemical shifts that accurately reflected the experimentally observed resonances. All of the new compounds were characterized in solution by using mass spectrometry, IR spectroscopy, and (1)H, (13)C, and (11)B NMR spectroscopy and their structural types were unequivocally established by crystallographic analysis of complexes 1, 2, 4, 9, and 10.