Interaction of Metal Oxido Compounds with B(C₆F₅)₃

Abstract

Lewis acid-base pair chemistry has been placed on an ew level with the discovery that adduct formationb etween an electron donor (Lewis base) and acceptor (Lewis acid) can be inhibited by the introductiono fs teric demand, thus preserving the reactivityo fb oth Lewis centers, resulting in highly unusual chemistry.S ome of these highly versatile frustrated Lewis pairs (FLP) are capable of splitting avariety of small molecules, such as dihydrogen, in ah eterolytic and even catalytic manner.T his is in sharp contrastt oc lassical reactions where the inert substrate must be activated by am etal-basedc atalyst. Very recently,r esearch has emerged combining the two concepts,n amely the formationo fF LPs in whichametal compound represents the Lewis base, allowing for novel chemistry by using the heterolytic splitting power of both together with the redox reactivity of the metal. Such reactivity is not restricted to the metal center itself being aL ewis acid or base, also ancillary ligandsc an be used as part of the Lewis pair,s till with the benefit of the redox-active metal centern earby. This Minireview is designed to highlight the novel reactions arising from the combination of metal oxido transition-metal or rare-earthmetal compounds with the Lewis acid B(C 6 F 5 ) 3 .I tc overs a wide area of chemistry including small molecule activation, hydrogenation and hydrosilylation catalysis, and olefin metathesis, substantiating the broad influence of the novel concept. Futureg oals of this young and excitinga rea are briefly discussed.

Reversible Activation of Water by an Air‐ and Moisture‐Stable Frustrated Rhodium Nitrogen Lewis Pair

“…Notably,a fter heating 3 at 393 Kfor 30 min about 30 %ofclean conversiont o2 was measured by 31 P{ 1 H} NMR spectroscopy,t hus indicating that 2 is a system capable of affording reversible uptake and releaseo f H 2 . [8,9] Complex 2 also activates the polar OÀHb ond of water.N otably,a ddition of excess of water to THF solutionso fc omplex 2 does not produce significant changes in its 1 Ha nd 31 PNMR spectra.H owever,N MR and MS measurements clearly indicate that complex 2 reacts with deuterated water in ar eversible fashion resulting in the deuteration of the Cp* group. The 31 P{ 1 H} NMR spectrum of [D 8 ]THF/D 2 O( 78 %/22 %, v/v) solutions does not change over time but the 1 HNMR spectrumw as found to be time-dependent.…”

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

“…Our previously described molybdenum oxido imido adducts [Mo{OB(C 6 F 5 ) 3 }(N t Bu)L 2 ] were found to catalyze the hydrosilylation of benzaldehyde [23,26] . We demonstrated that benzaldehyde inserts into the B−H bond during catalysis.…”

“…Our previously described molybdenum oxido imido adducts [Mo{OB(C 6 F 5 ) 3 }(N t Bu)L 2 ] were found to catalyze the hydrosilylation of benzaldehyde. [ 23 , 26 ] We demonstrated that benzaldehyde inserts into the B−H bond during catalysis. Similar observations were made recently in the hydrosilylation of carbonyl compounds catalyzed by hydridoborenium borate salts, where also insertion into the B−H bond was observed.…”

“…[24] While the frustrated Lewis pair concept has its important merits in the development of metal-free catalysis, the interaction of bulky Lewis acids and bases can be extended to metal-containing systems thereby significantly broadening the possibilities. The metal center maybe directly involved in the FLP, [25] or one of the ligands plays a role, for example a metal oxido group being the Lewis base in the FLP [26] which is well demonstrated by the Ison group. [27] Even both together, metal center and coordinated ligand, can be modulated as FLP in a bifunctional complex.…”

Assessing Combinations of B(C6F5)3 and N2‐Derived Molybdenum Nitrido Complexes for Heterolytic Bond Activation

“…We commenced our investigations by checking the stability of N MoN and P MoN with the strong Lewis acid (LA) B(C 6 F 5 ) 3 . Treating solutions thereof in either deuterated benzene or toluene with an equimolar amount of B(C 6 F 5 ) 3 at room temperature immediately led to the quantitative formation of the new compounds N 1 and P 1 according to NMR ( 1 H, 11 B, 19 F and 31 P) analysis (Scheme 1). For both Mo compounds, the boron resonance of B(C 6 F 5 ) 3 in the 11 B NMR spectra was strongly shifted to higher fields, from 58 to 4 and À 5 ppm when complexed to N MoN and P MoN, respectively.…”