Rongala Ramalakshmi

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.

New Heteronuclear Bridged Borylene Complexes That Were Derived from [{Cp*CoCl}2] and Mono-MetalCarbonyl 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.

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.

Reactivity of [Cp*Mo(CO)3Me] with chalcogenated borohydrides Li[BH2E3] and Li[BH3EFc] (Cp*= (η5-C5Me5); E = S, Se or Te; Fc = (C5H5-Fe-C5H4))

AbstractReactivity of [Cp*Mo(CO) 3Me], 1 with various chalcogenide ligands such as Li[BH 2E3] and Li[BH 3EFc] (E = S, Se or Te; Fc = (C 5H5-Fe-C 5H4)) has been described. Room temperature reaction of 1 with Li[BH 2E3] (E = S and Se) yielded metal chalcogenide complexes [Cp*Mo(CO) 2(η2-S 2CCH3)], 2 and [Cp*Mo(CO) 2(η1-SeC 2H5)], 3. In compound 2, {Cp*Mo(CO) 2} fragment adopts a four-legged piano-stool geometry with a η2-dithioacetate moiety. In contrast, treatment of 1 with Li[BH 3(EFc)] (E = S, Se or Te; Fc = C 5H5-Fe-C 5H4) yielded borate complexes [Cp*Mo(CO) 2(μ-H)(μ-EFc)BH 2], 4-6 in moderate yields. Compounds 4-6 are too unstable and gradual conversion to [{Cp*Mo(CO) 2} 2(μ-H)(μ-EFc] (7: E = S; 8: Se) and [{Cp*Mo(CO) 2} 2(μ-TeFc) 2], 9 happened by subsequent release of BH 3. All the compounds have been characterized by mass spectrometry, IR, multinuclear NMR spectroscopy and structures were unequivocally established by crystallographic analysis for compounds 2, 3 and 7. Graphical AbstractReactivity of [Cp*Mo(CO)3Me] with various chalcogenide ligands such as, Li[BH2E3] and Li[BH3EFc] (E = S, Se or Te; Fc = (C5H5-Fe-C5H4)), generated novel molybdenum thiolate and agostic borate complexes respectively.

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.

Dimetallaheteroborane clusters containing group 16 elements: A combined experimental and theoretical study

AbstractRecently we described the synthesis and structural characterization of various dimetallaherteroborane clusters, namely nido-[(Cp∗Mo)2B4EClxH6−x], 1–3; (1: E = S, x = 0; 2: E = Se, x = 0; 3: E = Te, x = 1). A combined theoretical and experimental study was also performed, which demonstrated that the clusters 1–3 with their open face are excellent precursors for cluster growth reaction. In this investigation process on the reactivity of dimetallaheteroboranes with metal carbonyls, in addition to [(Cp∗Mo)2B4H6EFe(CO)3] (4: E = S, 6: E = Te) reported earlier, reaction of 2 with [ Fe2(CO)9] yielded mixed-metallaselenaborane [(Cp∗Mo)2B4H6SeFe(CO)3], 5 in good yield. The quantum chemical calculation using DFT method has been carried out to probe the bonding, NMR chemical shifts and electronic properties of dimolybdaheteroborane clusters 4–6. Graphical AbstractDuring the course of our investigation on the reactivity of dimetallaheteroboranes with metal carbonyls, in addition to [(Cp*Mo)2B4H6EFe(CO)3] (E = S, Te) reported earlier, reaction of [(Cp*Mo)2B4H6Se] with [Fe2(CO)9] yielded mixed-metallaselenaborane [(Cp*Mo)2B4H6SeFe(CO)3], in good yield.