Half-Sandwich Iron(II) and Ruthenium(II) Complexes with the Dicarbollylamino Ligand System

Charge-compensated nido-carborane derivatives in the synthesis of iron(II) bis(dicarbollide) complexes

A series of stable iron(II) bis(dicarbollide) derivatives [8,8'-(RNHC(Et)HN)2-3,3'-Fe(1,2-C2B9H10)2] (R = Pr, R = Ph, (CH2)2OH, (CH2)3OH, (CH2)2NMe2) was prepared starting from FeCl2 or [FeCl2(dppe)] and the corresponding nido-carboranyl amidines [10-RNHC(Et)HN-7,8-C2B9H11]. In a similar way, the reactions of the oxonium derivatives of nido-carborane with FeCl2 in tetrahydrofuran in the presence of t-BuOK lead to the corresponding stable oxonium derivatives iron(II) bis(dicarbollide) [8,8'-(RR'O)2-3,3'-Fe(1,2-C2B9H10)2] (RR' = (CH2)4, (CH2)2O(CH2)2, (CH2)5; R = R' = Et), which can be alternatively prepared by the reaction of the parent iron(II) bis(dicarbollide) with tetrahydrofuran or 1,4-dioxane in the presence of Me2SO4. The cyclic voltammetry studies of the synthesized iron(II) bis(dicarbollide) derivatives revealed that the introduction of amidinium and oxonium substituents leads to a significant increase in the Fe2+/Fe3+ redox potential relative to the parent iron(II) bis(dicarbollide). The redox potentials of the oxonium derivatives are close to the redox potential of ferrocene and somewhat lower than redox potentials of sulfonium and phosphonium derivatives of iron(II) bis(dicarbollide).

Half-Sandwich Nickelacarboranes Derived from [7-(MeO(CH2)2S)-7,8-C2B9H11]−

New carboranyl thioethers 1-MeO(CH2)nS-1,2-C2B10H11 (n = 2, 3) were prepared by the alkylation of the trimethylammonium salt of 1-mercapto-ortho-carborane with 1-bromo- 2-methoxyethane and 1-bromo-3-methoxypropane, respectively. Their deboronation with cesium fluoride in ethanol gave the corresponding nido-carboranes Cs[7-MeO(CH2)nS-7,8-C2B9H11] (n = 2, 3). The reactions of Cs[7-MeO(CH2)2S-7,8-C2B9H11] with various nickel(II) phosphine complexes [(dppe)NiCl2] and [(R’R2P)2NiCl2] (R = R’ = Ph, Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) were studied and a series of nickelacarboranes 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 and 3,3- (R’R2P)2-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 (R = R’ = Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) was prepared. The molecular crystal structure of 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 was determined by single-crystal X-ray diffraction.

Synthesis and crystal structures of nickel(ii) and palladium(ii) complexes with o-carboranyl amidine ligands

A number of new nido-carboranyl amidines 10-R(CH₂)_nNHC(Et)[double bond, length as m-dash]HN-7,8-C₂B₉H₁₁ (n = 2, R = OH, OMe, and NMe₂; n = 3, R = OH) were synthesized by the nucleophilic addition of amino alcohols and N,N-dimethylethylenediamine to the highly activated -C[triple bond, length as m-dash]N⁺- triple bond of the 10-propionitrilium derivative of nido-carborane. A similar reaction of 10-EtC[triple bond, length as m-dash]N-7,8-C₂B₉H₁₁ with ethylenediamine unexpectedly resulted in the cleavage of the C[triple bond, length as m-dash]N bond to form the ammonium derivative 10-H₃N-7,8-C₂B₉H₁₁. The complexation of the synthesized carboranyl amidines 10-MeO(CH₂)₂NHC(Et)[double bond, length as m-dash]HN-7,8-C₂B₉H₁₁ and 10-Me₂N(CH₂)₂NHC(Et)[double bond, length as m-dash]HN-7,8-C₂B₉H₁₁ with nickel and palladium phosphine complexes [(Ph₃P)₂MCl₂] (M = Ni, Pd) was studied. The reactions with 10-MeO(CH₂)₂NHC(Et)[double bond, length as m-dash]HN-7,8-C₂B₉H₁₁ result in half-sandwiched metallacarborane complexes with the retention of one triphenylphosphine ligand [3-Ph₃P-3-(8-MeOCH₂CH₂N[double bond, length as m-dash]C(Et)NH)-3,1,2-MC₂B₉H₁₀], while the reactions with 10-Me₂N(CH₂)₂NHC(Et)[double bond, length as m-dash]HN-7,8-C₂B₉H₁₁ proceed with the complete loss of the phosphine ligands and lead to the formation of complexes with the η⁵:κ²(N,N')-coordinated carboranyl amidine ligand [3,3-(8-Me₂NCH₂CH₂N[double bond, length as m-dash]C(Et)NH)-3,1,2-MC₂B₉H₁₀]. The crystal molecular structures of the synthesized complexes were determined by single crystal X-ray diffraction.

Synthesis, structural characterization, and reactivity of Group 4 metallacarboranes bearing the ligand [H2C(C5Me4)(C2B9H10)]3-

A new organic-inorganic hybrid ligand H(2)C(C(5)Me(4)H)(C(2)B(10)H(11)) (2) has been prepared. A selective deboration reaction with piperidine in ethanol resulted in the isolation of [Me(3)NH][H(2)C(C(5)Me(4)H)(C(2)B(9)H(11))] (3). An amine-elimination reaction of 3 with [Zr(NMe(2))(4)] produced a neutral metal-amide complex [η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))]Zr(NMe(2))(NHMe(2)) (4). The double-ring-opening reaction of 4 with tetrahydrofuran (THF) afforded [η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))]Zr (OCH(2)CH(2)CH(2)CH(2))(2)N(CH(3))(2) (5). Treatment of the trianionic salt of 3 with [MCl(4)(thf)(2)] gave complexes [{η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))}M(μ-Cl)(2)][Li(thf)(2)] (M=Zr (6), Hf (7)). Reaction of 6 with LiCH(2)TMS generated the ionic species [{η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))}Zr(CH(2)TMS)(2)][Li(thf)(3)] (9). Interaction of complex 6 with KCH(2)(NMe(2))-o-C(6)H(4) led to the formation of the neutral metal alkyl complex [η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))]Zr[σ:σ-CH(2)(NMe(2))-o-C(6)H(4)] (10). All complexes have been fully characterized by various spectroscopic techniques and elemental analyses. Some were further confirmed by single-crystal X-ray analyses.

Synthesis of Functional Derivatives of 7,8-Dicarba-nido-undecaborate Anion by Ring-Opening of Its Cyclic Oxonium Derivatives

A new approach to synthesis of functional derivatives of 7,8-dicarba-nido-undecaborate anion based on ring-opening of its cyclic oxonium derivatives [10-(CH2)4O-7,8-C2B9H11] and [10-O(CH2CH2)2O-7,8-C2B9H11] with various nucleophiles was developed. Both cyclic oxonium derivatives can be obtained as single isomers by reaction of the parent anion [7,8-C2B9H12]- with mercury(II) chloride in the corresponding solvents. Mechanism of formation of the cyclic oxonium derivatives of 7,8-dicarba-nido-undecaborate anion was proposed. A series of 7,8-dicarba-nido-undecaborate derivatives with terminal carboxylic and azide functions were prepared by the ring-opening reactions of the cyclic oxonium derivatives with substituted phenolate and azide ions, respectively.

Synthesis and structural characterization of mono- and bisfunctional o-carboranes

Functionalized o-carboranes are interesting ligands for transition metals. Reaction of LiC2B10H11 with Me2NCH2CH2Cl in toluene afforded 1-Me2NCH2CH2-1,2-C2B10H11 (1). Treatment of 1 with 1 equiv. of n-BuLi gave [(Me2NCH2CH2)C2B10H10]Li ([1]Li), which was a very useful synthon for the production of bisfunctional o-carboranes. Reaction of [1]Li with RCH2CH2Cl afforded 1-Me2NCH2CH2-2-RCH2CH2-1,2-C2B10H10 (R = Me2N (2), MeO (3)). 1 and 2 were also prepared from the reaction of Li2C2B10H10 with excess Me2NCH2CH2Cl. Treatment of [1]Li with excess MeI or allyl bromide gave the ionic salts, [1-Me3NCH2CH2-2-Me-1,2-C2B10H10][I] (4) and [1-Me2N(CH2=CHCH2)CH2CH2-2-(CH2=CHCH2)-1,2-C2B10H10][Br] (6), respectively. Interaction of [1]Li with 1 equiv. of allyl bromide afforded 1-Me2NCH2CH2-2-(CH2=CHCH2)-1,2-C2B10H10 (5). Treatment of [1]Li with excess dimethylfulvene afforded 1-Me2NCH2CH2-2-C5H5CMe2-1,2-C2B10H10 (7). Interaction of [1]Li with excess ethylene oxide afforded an unexpected product 1-HOCH2CH2-2-(CH2=CH)-1,2-C2B10H10 (8). 1 and 3 were conveniently converted into the corresponding deborated compounds, 7-Me2NHCH2CH2-7,8-C2B9H11 (9) and 7-Me2NHCH2CH2-8-MeOCH2CH2-7,8-C2B9H10 (10), respectively, in MeOH-MeOK solution. All of these compounds were characterized by various spectroscopic techniques and elemental analyses. The solid-state structures of 4 and 6-10 were confirmed by single-crystal X-ray analyses.

Sulfur, tin and gold derivatives of 1-(2′-pyridyl)-ortho-carborane, 1-R-2-X-1,2-C2B10H10(R = 2′-pyridyl, X = SH, SnMe3or AuPPh3)

Reaction of the lithium salt of 1-(2'-pyridyl)-ortho-carborane, Li[1-R-1,2-C(2)B(10)H(10)](R = 2'-NC(5)H(4)), with sulfur, followed by hydrolysis, gave the mercapto-o-carborane, 1-R-2-SH-1,2-C(2)B(10)H(10) which forms chiral crystals containing helical chains of molecules linked by intermolecular S-H...N hydrogen bonds. The cage C(1)-C(2) and exo C(2)-S bond lengths (1.730(3) and 1.775(2)[Angstrom], respectively) are indicative of exo S=C pi bonding. The tin derivative 1-R-2-SnMe(3)-1,2-C(2)B(10)H(10), prepared from Li[1-R-1,2-C(2)B(10)H(10)] and Me(3)SnCl, crystallises with no significant intermolecular interactions. The pyridyl group lies in the C(1)-C(2)-Sn plane, oriented to minimise the NSn distance (2.861(3)[Angstrom]). The tin environment is distorted trigonal bipyramidal with axial N and Me. The gold derivative 1-R-2-AuPPh(3)-1,2-C(2)B(10)H(10), prepared from Li[1-R-1,2-C(2)B(10)H(10)] and AuCl(PPh(3)), reveals no NAu interaction in its crystal structure.

Novel titanium complexes of a multidentate dicarbollide ligand. Synthesis and structural characterization of a constrained geometry complex

The multidentate dicarbollide ligand nido-7,8-(NMe2CH2)2-7,8-C2B9H11 has been prepared, structurally characterized, and employed in the preparation of the novel mono- and trimetallic titanium complexes [eta5:eta1-(NMe2CH2)C2B9H9CH2NMe2]Ti(NMe2)2 and [eta5:eta1-[(NMe2CH2)C2B9H9CH2NMe2]Ti(NMe2)]2-mu3-O-Ti(NMe2)2.