Boronyl Ligand as a Member of the Isoelectronic Series BO− → CO → NO+: Viable Cobalt Carbonyl Boronyl Derivatives?

Structural Trends in Monoboronyl Compounds: Analysis of the Interaction of Second-Row Elements with BO

A theoretical study of the monoboronyl compounds of second-row elements, [XBO] (X = Na, Si, P, S, Cl), has been carried out. It is observed that the preference for the XBO arrangement is higher when moving to the right of the period. In the case of sodium monoboronyl three minima were characterized, all lying rather close in energy: linear NaBO, linear NaOB, and an L-shaped structure. Linear NaBO and the L-shaped structure are nearly isoenergetic, whereas linear NaOB is located 2.11 kcal/mol above linear NaBO. The barrier for the conversion of the L-shaped structure into linear NaBO is about 5.1 kcal/mol, suggesting that both species could be potential targets for experimental detection. For silicon monoboronyl, two minima, linear SiBO and linear SiOB, are found, the latter lying about 13 kcal/mol above SiBO. The barrier for the isomerization of SiOB into SiBO is estimated to be 11.4 kcal/mol. For phosphorus, sulfur, and chlorine monoboronyls the linear XBO isomer is clearly the most stable one, and the barriers for the conversion into XOB species are relatively high, suggesting that quite likely the linear XBO isomer should be the main experimental target. All studied monoboronyls are relatively stable, with dissociation energies increasing from left to right of the second-row (69.8 kcal/mol for NaBO and 118.98 kcal/mol for ClBO). An analysis of the bonding for second-row monoboronyls has been carried out, emphasizing the different characteristics of the X-B and X-O bonds along the second row.

The siliconyl, boronyl, and iminoboryl ligands as analogues of the well-known carbonyl ligand: predicted reactivity towards dipolar cyclooligomerization in iron/cobalt carbonyl complexes

The Fe(CO)₄(SiO), Co(CO)₄(BO), and Co(CO)₄(BNSiMe₃), complexes akin to the well-known Fe(CO)₅ are predicted by density functional theory to undergo exothermic oligomerization to give the oligomers containing Si_nO_n/B_nO_n/B₂N₂ rings with single bonds.

B═B and B≡E (E = N and o) multiple bonds in the coordination sphere of late transition metals

Because of their unusual structural and bonding motifs, multiply bonded boron compounds are fundamentally important to chemists, leading to enormous research interest. To access these compounds, researchers have introduced sterically demanding ligands that provide kinetic as well as electronic stability. A conceptually different approach to the synthesis of such compounds involves the use of an electron-rich, coordinatively unsaturated transition metal fragment. To isolate the plethora of borane, boryl, and borylene complexes, chemists have also used the coordination sphere of transition metals to stabilize reactive motifs in these molecules. In this Account, we summarize our results showing that increasingly synthetically challenging targets such as iminoboryl (B≡N), oxoboryl (B≡O), and diborene (B═B) fragments can be stabilized in the coordination sphere of late transition metals. This journey began with the isolation of two new iminoboryl ligands trans-[(Cy3P)2(Br)M(B≡N(SiMe3))] (M = Pd, Pt) attached to palladium and platinum fragments. The synthesis involved oxidative addition of the B-Br bond in (Me3Si)2N═BBr2 to [M(PCy3)2] (M = Pt, Pd) and the subsequent elimination of Me3SiBr at room temperature. Variation of the metal, the metal-bound coligands, and the substituent at the nitrogen atom afforded a series of analogous iminoboryl complexes. Following the same synthetic strategy, we also synthesized the first oxoboryl complex trans-[(Cy3P)2BrPt(BO)]. The labile bromide ligand adjacent to platinum makes the complex a viable candidate for further substitution reactions, which led to a number of new oxoboryl complexes. In addition to allowing us to isolate these fundamental compounds, the synthetic strategy is very convenient and minimizes byproducts. We also discuss the reaction chemistry of these types of compounds. In addition to facilitating the isolation of compounds with B≡E (E = N, O) triple bonds, the platinum fragment can also stabilize a diborene (RB═BR) moiety, a bonding motif that thus far had only been accessible when stabilized by N-heterocyclic carbenes (NHCs). In the new π-diborene [(Et3P)2Pt(B2Dur2)] (Dur = 2,3,5,6-Me4-C6H) complex, the diborene ligand receives electron density from Pt, leading to a strong Pt-B bond and a B═B bond. We attribute this result to the very short B═B bond distance (1.51(2) Å) while coordinated to platinum. Overall, an increasing number of chemists are examining the chemistry of multiply bound boron compounds. The isolation of an oxoboryl complex is of special interest not only from a structural standpoint but also because of its orbital similarities to the ubiquitous CO ligand. Detailed computational studies of the π-diborene complex [(Et3P)2Pt(B2Dur2)] show that the bonding properties of this molecule violate the widely accepted Dewar-Chatt-Duncanson (DCD) bonding model.