We report herein the use of the (dihydrido)iron catalyst, Fe(H)2(dmpe)2, for the selective reduction of CO2 into either bis(boryl)acetal or methoxyborane depending on the hydroborane used as a reductant. In a one-pot two-step procedure, the in situ generated bis(boryl)acetal was shown to be a reactive and versatile source of methylene to create new C-N but also C-O and C-C bonds.

To use carbon dioxide as a source of carbon, recent progress has been made toward the synthesis of higher value chemicals and in particular toward Cn compounds. In this context, we report here the synthesis of a borylated C3‐carbohydrate from CO2 as the only source of carbon. This result corresponds to the unprecedented formation of a polyol chain and of asymmetric carbon atoms from CO2. The adopted strategy involves the Fe‐catalysed selective 4e− reduction of CO2 into bis(boryl)acetal followed in one‐pot by a carbene‐mediated C−C coupling reaction. Boron is shown to play a key role in the coupling step enabling to observe the first diastereoselective formose‐type reaction. This result is in addition obtained under mild reaction conditions (T<80 °C, 1 atm of CO2) and short reaction time (t<2 h).

Despite their relative scarcity, agostic complexes in which a C À C, [1] rather than a C À H, bond apparently interacts with a main-group or transition metal have been attracting much attention recently. This stems mainly from their involvement in metallacyclobutanes, which are intermediates in alkene metathesis reactions, [2] and also in their ability to model C À C s-complexes and C À C bond cleavage.[3] We have characterized a series of a-C À C agostic cyclopropyl complexes [Tp Me2 NbX(c-C 3 H 5 )(MeCCMe)] (X = Cl, Me, etc.) by different methods including X-ray diffraction, solution NMR and DFT modeling.[4] The poor overlap between the C orbitals within the strained C3 ring was suggested to be responsible for the preference of an a-CC over more classical a-or b-CH agostic distortions. [4b,c, 5] The elongation of the a-CC agostic bond was accompanied by a lowering of the associated J CC NMR spectroscopy coupling constant.[1j, 2, 4a] We also successfully calculated these J CC values, realizing that computation is a reliable alternative to the inherently difficult problem of measuring J CC values.[4a] We report herein an unprecedented example of a heterobimetallic complex [Cp* 2 Y(m-c-C 3 H 5 ) 2 Li-(thf)] (1; Cp* = C 5 Me 5 ) that exhibits two different a-CC agostic distortions. We also discuss the nature of these distortions, showing that the a-CC agostic interaction with yttrium has a covalent nature whereas that with lithium has an electrostatic character.The complex [Cp* 2 Y(m-c-C 3 H 5 ) 2 Li(thf)] (1) is obtained as white crystals in 75 % yield by treatment of [Cp* 2 YCl(thf)] with two equivalents of Li-c-C 3 H 5 in diethyl ether (Scheme 1). Its formulation comes from analytical, spectroscopic, and Xray diffraction data. X-Ray diffraction on a single crystal reveals an unexpected unsymmetrical structure (Figure 1). [6] The yttrium is in a typical bent metallocene environment while the lithium is formally three coordinate. The yttrium and the lithium are bridged by two cyclopropyl groups by C1 (group A) and C4 (group B) with a puckered Y1-C1-Li1-C4 ring (488 between Y1-C1-C4 and Li1-C1-C4 planes). The bond lengths between these Ca and yttrium are unexceptional even if Y1 À C1 is slightly longer than Y1 À C4 [Y1-C1 2.477(5), Y1-C4 2.432 (5)

The synthesis of a stable lithium phosphonium-sulfinyl yldiide was explored. The compound was fully characterized by NMR spectroscopy and X-ray crystallography. The electronic structure of 2 was analyzed by DFT calculations, which indicated strong ylidic character. Yldiide 2 was stable enough [a]

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The synthesis of a novel family of cyclic push-pull carbenes, namely, azavinylidene phosphoranes, is described. The methodology is based on a formal [3+2] cycloaddition between terminal alkynes and phosphine-imines followed by an oxidation/deprotonation step. Carbenes 6, obtained by simple deprotonation, exhibit typical transient carbene reactivity like the intramolecular CH insertion reaction and a pronounced ambiphilic character exemplified by [2+1] cycloaddition with electron-poor methyl acrylate. Owing to the cyclic structure, carbenes 6 also exhibit an excellent coordination ability toward transition metals. Rh(I) complex 10 was obtained in excellent yield and was fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The corresponding Rh(I) -carbonyl complex was also prepared; this indicates that carbenes 6 belong to the strongest σ-donating ligands to date. DFT calculations confirmed the high σ-donation ability of 6 and their classification as push-pull carbenes with a relatively small singlet-triplet energy gap of 23.2-24.3 kcal mol(-1) .

Based on the use of a (dihydrido)iron complex as catalyst the conversion of hydroboranes to bis(boryl)acetal (III) using CO2 as one‐carbon source is optimized.

Two better than one! The structural distortions in a bis(cyclopropyl) heterobimetallic lithium yttrium complex can be interpreted as two types of CC agostic interactions (see structure), one with a more covalent character with Y, the other with a more electrostatic character with Li. The CC agostic interaction with Y is reinforced by a CH agostic interaction.