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Strongly phosphorescent transition metal Ļ complexes of boron-boron triple bonds
Herein are reported the first Ļ complexes of compounds with boron-boron triple bonds to transition metals, in this case CuI. Three different compounds were isolated that differ in the number of copper atoms bound to the BB unit. Metallation of the B-B triple bonds causes significant lengthening of the B-B and B-CNHC bonds, as well as large upfield shifts of the 11B NMR signals, suggesting greater orbital interactions between the boron and transition metal atoms than those observed with recently published diboryne / alkali metal cation complexes. In contrast to previously-reported fluorescent copper(I) Ļ complexes of boron-boron double bonds, the Cun-Ļ-diboryne compounds (n = 2, 3) show intense phosphorescence in the red to near-IR region from their triplet excited states, according to their microsecond lifetimes, with quantum yields of up to 58%. The bonding situation, as well as the unusual photophysical properties, has been further corroborated by DFT studies
Synthesis and characterization of a mercury-containing metalloborylene
The reaction of phenylmercuric chloride with an anionic dimanganaborylene [Cp2(CO)4Mn2B]Na led to the formation and isolation of a trimetalloborylene featuring at previously unreported bond between mercury and a single boron atom. Examination by 199Hg NMR displayed a small 11B-199Hg scalar coupling (J = 103 Hz), confirming the electronic interaction of the two atoms. The use of ETS-NOCV analysis indicated the nature of bonding to be Ļ-donation from a B-Mn Ļ-orbital to Hg, in conjunction with weak HgdāĻ* back-donation
Understanding, Modulating, and Leveraging Transannular M ā Z Interactions
Density functional theory calculations have been performed on metallatranes featuring a group 13 elements at the bridgehead position to understand the factors that influence the nature of the MĀ·Ā·Ā·Z (M = Fe, Co, Ni; Z = Al, Ga, In) interaction present in these complexes and the resultant reactivity at the metal center. The strength of the MĀ·Ā·Ā·Z interaction increases with the increase in the size and polarizability of the bridgehead group 13 elements. The calculated reaction free energies (ĪGĀ° values) for binding of different Lewis bases to the metallatranes are found to be significantly more exergonic for the larger In(III) ions. Quantum theory of atoms in molecules calculations reveal the covalent nature of the MĀ·Ā·Ā·Z interactions, while the EDA-NOCV analysis indicates the strong binding ability of these metallatranes not only to different Ļ-donor and Ļ-acceptor ligands but also to relatively inert species, such as N2
Theoretical Study on the Effect of Annelation and Carbonylation on the Electronic and Ligand Properties of <i>N</i>āHeterocyclic Silylenes and Germylenes: Carbene Comparisons begin To Break Down
Quantum
chemical calculations have been carried out to investigate
the effect of annelation and carbonylation on the electronic and ligand
properties of <i>N</i>-heterocyclic silylenes and germylenes.
The thermodynamic stability of these ligands has been found to increase
with annelation, while the reverse is true for carbonylation. This
is in sharp contrast to N-heterocyclic carbenes (NHCs) where annelation
leads to a decrease in their thermodynamic stabilities. Compared to
nonannelated derivatives, annelated and carbonylated ones are found
to be weaker Ļ donors but better Ļ acceptors. The effect
of carbonylation is more pronounced than annelation toward increasing
the Ļ acidity of these ligands. Carbonylation at the Ī±-position
with respect to the N atom attached to the Si/Ge center has been found
to be the most effective way of enhancing the Ļ acidity of these
ligands. The computed natural charges reveal that electrophilicity
increases upon both annelation and carbonylation. The calculated values
of <sup>31</sup>P NMR chemical shifts of corresponding phosphinidene
adducts of these ligands have been found to correlate well with the
Ļ acidity of these Si/Ge centers
Tuning the Electronic and Ligand Properties of Remote Carbenes: A Theoretical Study
The
effect of annulation and carbonylation on the electronic and
ligating properties of remote N-heterocyclic carbenes (rNHCs) has
been studied quantum-chemically. The thermodynamic stability of these
complexes has been assessed on the basis of their hydrogenation and
stabilization energies, while HOMOāLUMO gaps are used to measure
the kinetic stabilities. Annulated/carbonylated rNHCs are found to
be weaker Ļ donors but better Ļ acceptors compared with
the parent rNHCs. The reactivity of these rNHCs has been studied by
evaluating their nucleophilicity and electrophilicity indices. The
nucleophilicity values are in good agreement with the Ļ basicities
of all of the rNHCs. The <sup>31</sup>P NMR chemical shifts of the
corresponding rNHCāphosphinidene adducts have been calculated
and found to correlate well with the Ļ acidities of these rNHCs
Ligand Properties of Boron-Substituted Fiveā, Sixā, and Seven-Membered Heterocyclic Carbenes: A Theoretical Study
The
electronic properties of boron-substituted five-, six-, and
seven-membered heterocyclic carbenes have been studied using quantum
chemical methods. The stability of carbenes has been examined from
the values of their respective singletātriplet and HOMOāLUMO
gaps. Both the singletātriplet and the HOMOāLUMO gaps
indicate higher stability for six- and seven-membered P-heterocyclic
carbenes (PHCs) containing boron atoms at the Ī± position with
respect to phosphorus atoms. While PHCs are better Ļ acceptors,
the Ļ acidities of NHCs can be tuned by substituting a boron
atom in the Ī± position with respect to nitrogen. This is revealed
by the energies of a Ļ-symmetric unoccupied orbital centered
at the central carbon atom. Reactivity of these carbenes has been
discussed in terms of nucleophilicity and electrophilicity index.
The calculated relative redox potential values and <sup>13</sup>C
NMR parameters are found to correlate well with the Ļ acidities
of the respective carbenes
Probing the Potential of Hitherto Unexplored Base-Stabilized Borylenes in Dinitrogen Binding
Computational investigations were carried out to probe the potential of several dicoordinate, singly base-stabilized borylenes of the form [LāBR] (L=neutral Lewis base) in dinitrogen binding. The calculated reaction free energies and activation barriers associated with the formation of mono- and diborylene-N2 adducts suggest the presence of thermally surmountable kinetic barriers towards their possible isolation. Our results show that the exergonicity of dinitrogen activation and fixation is linearly dependent on the natural charge at the boron center, which can be tuned to design novel boron-based compounds with potential applications to small-molecule activation. EDA-NOCV analysis reveals strong binding of dinitrogen to these base-stabilized borylenes
Nature of Intramolecular MetalāMetal Interactions in Supported Group 4āGroup 9 and Group 6āGroup 9 Heterobimetallic Complexes: A Combined Density Functional Theory and Topological Study
Quantum chemical calculations have been carried out on
a series
of supported group 4āgroup 9 and group 6āgroup 9 heterobimetallic
complexes designated by the general formulas [Cp<sub>2</sub>MĀ(Ī¼-E)<sub>2</sub>Mā²(H)Ā(CO)ĀL] and [(CO)<sub>4</sub>MĀ(Ī¼-E)<sub>2</sub>Mā²(H)Ā(CO)ĀL] where E = SH, SeH or PH<sub>2</sub> and L = PH<sub>3</sub>, CO, NHC, or <i>a</i>NHC. An analysis of the optimized
geometries of these molecules indicates the presence of an MĀ·Ā·Ā·Mā²
interaction. The nature of this interaction is investigated by using
Baderās quantum theory of atoms in molecules (QTAIM), electron
localization function (ELF), and source function (SF). The results
of QTAIM analysis suggest a polar covalent interaction between the
two disparate metal centers in these heterobimetallic complexes. ELF
analysis identifies a bonding basin between the two metal centers,
while SF analysis reveals that the metalāmetal bonding is moderately
delocalized. The strength of the MĀ·Ā·Ā·Mā² interaction
is found to be stronger in group 4āgroup 9 heterobimetallic
complexes compared to group 6āgroup 9 ones
Spectroscopic Distinction of Different Carbon Bases: An Insight from Theory
Spectroscopic
differentiation based on the <sup>13</sup>C NMR chemical shift of
the parent and protonated derivatives of carbonĀ(II) and carbon(0)
bases has been proposed. The <sup>13</sup>C chemical shift of the
central carbon atom of carbenes in their parent and protonated forms
will experience more downfield shift, whereas the central carbon atom
of carbones will experience a lesser downfield shift; such shifts
for compounds that possess āhiddenā carbon(0) characteristics
will lie between these two extremes. The <sup>13</sup>C chemical shifts
of the protonated derivatives are solely dependent on the out-of-plane
p<sub>Ļ</sub> occupancies of the central carbon atom. This difference
arises due to their unique difference in bonding and may provide an
easier distinction between these two classes of compounds