(BB)-Carboryne Complex of Ruthenium: Synthesis by Double B-H Activation at a Single Metal Center

The first example of a transition metal (BB)-carboryne complex containing two boron atoms of the icosahedral cage connected to a single exohedral metal center (POBBOP)Ru(CO)2 (POBBOP = 1,7-OP(i-Pr)2-2,6-dehydro-m-carborane) was synthesized by double B-H activation within the strained m-carboranyl pincer framework. Theoretical calculations revealed that the unique three-membered (BB)>Ru metalacycle is formed by two bent B-Ru σ-bonds with the concomitant increase of the bond order between the two metalated boron atoms. The reactivity of the highly strained electron-rich (BB)-carboryne fragment with small molecules was probed by reactions with electrophiles. The carboryne-carboranyl transformations reported herein represent a new mode of cooperative metal-ligand reactivity of boron-based complexes

Formation of a Cationic Vinylimido Group upon C–H Activation of Nitriles by Trialkylamines in the Presence of TaCl₅

We report a new CH₃CN activation mode where an imido group is directly formed by deprotonation of the nitrile coordinated to the highly Lewis acidic Ta^V center. The unexpected deprotonation of TaCl₅(CH₃CN) by NEt₃ resulted in isolation of the triethylammonium vinylimido complex [HNEt₃]­[Ta­(NC­(CH₂)­NEt₃)­Cl₅]. The reaction is proposed to proceed through rearrangement of the initial nucleophilic carbanion to the electrophilic azaallene/carbocation intermediate. The use of more sterically hindered (<i>i</i>-Pr)­CN and weakly nucleophilic N­(<i>i</i>-Pr)₂Et resulted in the isolation of a vinylimido group formed upon dimerization of deprotonated nitriles, suggesting deprotonation as the first step of the transformation

Metal- and Ligand-Centered Reactivity of <i>meta</i>-Carboranyl-Backbone Pincer Complexes of Rhodium

We report the synthesis of the chelating phosphinite-arm carboranyl POBOP-H (POBOP = 1,7-OP­(<i>i</i>-Pr)₂-<i>m</i>-carboranyl) ligand precursor, preparation of its rhodium complexes, and their reactivity in oxidative addition/reductive elimination reactions. The oxidative addition of iodobenzene to the low-valent (POBOP)­Rh­(PPh₃) resulted in the selective formation of the 16-electron complex (POBOP)­Rh­(Ph)­(I), featuring a highly strained exohedral rhodium–boron bond. The complex (POBOP)­Rh­(Ph)­(I) is the first example of a B-carboranyl aryl metal complex, which is a proposed intermediate in metal-promoted B–C coupling reactions. The complex (POBOP)­Rh­(Ph)­(I) was selectively and directly converted, in the presence of acetonitrile, to (POB­(BPh)­OP)­Rh­(H)­(I)­(CH₃CN) (POB­(BPh)­OP = 1,7-OP­(<i>i</i>-Pr)₂-2-Ph-<i>m</i>-carboranyl) through unprecedented cascade reductive elimination of the phenyl-<i>B</i>-carboranyl and the oxidative addition of a vicinal B–H bond of the boron cluster to the metal center, exhibiting both metal- and cluster-centered reactivity

Opening of Carborane Cages by Metal Cluster Complexes: The Reaction of a Thiolate-Substituted Carborane with Triosmium Carbonyl Cluster Complexes

The reaction of Os₃(CO)₁₀(NCMe)₂ with closo-<i>o</i>-(1-SCH₃)­C₂B₁₀H₁₁ has yielded the complex Os₃(CO)₉[μ₃-η³-C₂B₁₀H₉(SCH₃)]­(μ-H)₂, <b>1</b>, by the loss of the two NCMe ligands and one CO ligand from the Os₃ cluster and the coordination of the sulfur atom and the activation of two B–H bonds with transfer of the hydrogen atoms to the cluster. Reaction of <b>1</b> with a second equivalent of Os₃(CO)₁₀(NCMe)₂ yielded the complex Os₃(CO)₉(μ-H)­[(μ₃-η³-1,4,5-μ₃-η³-6,10,11-C₂B₁₀H₈S­(CH₃)]­Os₃(CO)₉(μ-H)₂, <b>2</b>, that contains two triosmium triangles attached to the same carborane cage. The carborane cage was opened by cleavage of two B–C bonds and one B–B bond. The B–H group that was pulled out of the cage became a triply bridging group on one of the Os₃ triangles but remains bonded to the cage by two B–B bonds. When heated to 150 °C, <b>2</b> was transformed into the complex Os₃(CO)₉(μ-H)­[(μ₃-η³-μ₃-η³-C₂B₁₀H₇S­(CH₃)]­Os₃(CO)₉(μ-H), <b>3</b>, by the loss of two hydrogen atoms and a rearrangement that led to further opening of the carborane cage. Reaction of <b>1</b> with a second equivalent of closo-<i>o</i>-(1-SCH₃)­C₂B₁₀H₁₁ has yielded the complex Os₃(CO)₆)­(μ₃-η³-C₂B₁₀H₉-<i>R</i>-SCH₃) (μ₃-η³-C₂B₁₀H₁₀-<i>S</i>-SCH₃)­(μ-H)₃, <b>4a</b>, containing two carborane cages coordinated to one Os₃ cluster. Compound <b>4a</b> was isomerized to the compound Os₃(CO)₆(μ₃-η³-C₂B₁₀H₉-<i>R</i>-SCH₃)­(μ₃-η³-C₂B₁₀H₁₀-<i>R</i>-SCH₃)­(μ-H)₃, <b>4b</b>, by an inversion of stereochemistry at one of the sulfur atoms by heating to 174 °C

(BB)-Carboryne Complex of Ruthenium: Synthesis by Double B–H Activation at a Single Metal Center

The first example of a transition metal (BB)-carboryne complex containing two boron atoms of the icosahedral cage connected to a single exohedral metal center (POBBOP)­Ru­(CO)₂ (POBBOP = 1,7-OP­(<i>i</i>-Pr)₂-2,6-dehydro-<i>m</i>-carborane) was synthesized by double B–H activation within the strained <i>m</i>-carboranyl pincer framework. Theoretical calculations revealed that the unique three-membered (BB)>Ru metalacycle is formed by two bent B–Ru σ-bonds with the concomitant increase of the bond order between the two metalated boron atoms. The reactivity of the highly strained electron-rich (BB)-carboryne fragment with small molecules was probed by reactions with electrophiles. The carboryne–carboranyl transformations reported herein represent a new mode of cooperative metal–ligand reactivity of boron-based complexes

(BB)-Carboryne Complex of Ruthenium: Synthesis by Double B–H Activation at a Single Metal Center

The first example of a transition metal (BB)-carboryne complex containing two boron atoms of the icosahedral cage connected to a single exohedral metal center (POBBOP)­Ru­(CO)₂ (POBBOP = 1,7-OP­(<i>i</i>-Pr)₂-2,6-dehydro-<i>m</i>-carborane) was synthesized by double B–H activation within the strained <i>m</i>-carboranyl pincer framework. Theoretical calculations revealed that the unique three-membered (BB)>Ru metalacycle is formed by two bent B–Ru σ-bonds with the concomitant increase of the bond order between the two metalated boron atoms. The reactivity of the highly strained electron-rich (BB)-carboryne fragment with small molecules was probed by reactions with electrophiles. The carboryne–carboranyl transformations reported herein represent a new mode of cooperative metal–ligand reactivity of boron-based complexes

Activation of C–H Bonds of Alkyl- and Arylnitriles by the TaCl₅–PPh₃ Lewis Pair

A new pathway of activation of C–H bonds of alkyl- and arylnitriles by a cooperative action of TaCl₅ and PPh₃ under mild conditions is reported. Coordination of nitriles to the highly Lewis acidic Ta­(V) center resulted in an activation of their aliphatic and aromatic C–H bonds, allowing nucleophilic attack and deprotonation by the relatively weak base PPh₃. The propensity of Ta­(V) to form multiple bonds to nitrogen-containing ligands is an important driving force of the reaction as it led to a sequence of bond rearrangements and the emergence of, in the case of benzonitrile, a zwitterionic enediimido complex of Ta­(V) through CC double bond formation between two activated nitrile fragments. These transformations highlight the special role of the high-valent transition metal halide in substrate activation and distinguish the reactivity of the TaCl₅–PPh₃ system from both non-metal- and late transition metal-based frustrated Lewis pairs

Stereospecific Ring-Opening Metathesis Polymerization of Norbornadienes Employing Tungsten Oxo Alkylidene Initiators

We report here the polymerization of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, stereoregular polymers. The tacticities of the menthyl ester derivatives of two polymers were determined for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not polymerized stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, stereoregular polymer was formed in the presence of 1 equiv of B(C6F5)3.United States. Dept. of Energy (DE-FG02- 86ER13564)Defense Threat Reduction Agency (DTRA) (Chemical and Biological Technologies, grant BA12PHM123 in the “Dynamic Multifunctional Materials for a Second Skin D[MS]2” program