We report the preparation of N‐heterocyclic carbene (NHC)‐stabilized compounds containing P=B double bonds. The reaction of the highly functionalized phosphinoborane Mes*(SiMe3)P−B(Cl)Cp* with Lewis ...bases allows access to base‐stabilized phosphinidene boranes Mes*P=B(L)Cp* (L=4‐dimethylaminopyridine (DMAP), NHC) by Me3SiCl elimination. The formation of these species is shown to proceed through transient borylphosphide anions generated by Me3Si ion.
Intermediate intercepted! Syntheses of a range of base‐stabilized P=B doubly‐bonded compounds proceeds by SiMe3 ion (see scheme; Mes*=2,4,6‐tri‐tert‐butylphenyl; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl). The interception of an anionic borylphosphide intermediate offers insight into thermal Me3SiCl elimination, for example in chemical vapor deposition processes.
Abstract
Covalency involving the 5f orbitals is regularly invoked to explain the reactivity, structure and spectroscopic properties of the actinides, but the ionic versus covalent nature of ...metal-ligand bonding in actinide complexes remains controversial. The tetrakis 2,6-di-
tert
-butylphenoxide complexes of Th, U and Np form an isostructural series of crystal structures containing approximately tetrahedral MO
4
cores. We show that up to 3 GPa the Th and U crystal structures show negative linear compressibility as the OMO angles distort. At 3 GPa the angles snap back to their original values, reverting to a tetrahedral geometry with an abrupt shortening of the M-O distances by up to 0.1 Å. The Np complex shows similar but smaller effects, transforming above 2.4 GPa. Electronic structure calculations associate the M-O bond shortening with a change in covalency resulting from increased contributions to the M-O bonding by the metal 6d and 5f orbitals, the combination promoting MO
4
flexibility at little cost in energy.
Abstract
A range of reasons has been suggested for why many low-coordinate complexes across the periodic table exhibit a geometry that is bent, rather a higher symmetry that would best separate the ...ligands. The dominating reason or reasons are still debated. Here we show that two pyramidal UX
3
molecules, in which X is a bulky anionic ligand, show opposite behaviour upon pressurisation in the solid state. UN″
3
(
UN3
, N″ = N(SiMe
3
)
2
) increases in pyramidalization between ambient pressure and 4.08 GPa, while U(SAr)
3
(
US3
, SAr = S-C
6
H
2
-
t
Bu
3
−2,4,6) undergoes pressure-induced planarization. This capacity for planarization enables the use of X-ray structural and computational analyses to explore the four hypotheses normally put forward for this pyramidalization. The pyramidality of
UN3
, which increases with pressure, is favoured by increased dipole and reduction in molecular volume, the two factors outweighing the slight increase in metal-ligand agostic interactions that would be formed if it was planar. The ambient pressure pyramidal geometry of
US3
is favoured by the induced dipole moment and agostic bond formation but these are weaker drivers than in
UN3
; the pressure-induced planarization of
US3
is promoted by the lower molecular volume of
US3
when it is planar compared to when it is pyramidal.
Formal exchange of C=C units with isoelectronic B=N or B=P units can provide access to molecules with unique electronic or chemical properties. Herein, we report the simple solution‐phase generation ...of highly reactive phosphaborenes, RP=BR, and demonstrate their use for the introduction of P=B units into organic systems. Ring opening of a P−B‐containing cyclobutene isostere provided access to unique 1,4‐boraphosphabutadiene systems with conjugated main‐group multiple bonds.
Captivating cousins: Transient phosphaborenes, RP=BR, can be generated in solution and used to introduce PB units into organic compounds as C=C isosteres (see scheme). A PB‐containing cyclobutene analogue underwent ring opening to give conjugated systems with main‐group multiple bonds.
Covalency is complex yet central to our understanding of chemical bonding, particularly in the actinide series. Here we assess covalency in a series of isostructural d and f transition element ...compounds M(OC
6
H
5
)
4
(M = Ti, Zr, Hf, Ce, Th, Pa, U, Np) using scalar relativistic hybrid density functional theory in conjunction with the Natural Bond Orbital (NBO), quantum theory of atoms in molecules (QTAIM) and interacting quantum atoms (IQA) approaches. The IQA exchange-correlation covalency metric is evaluated for the first time for actinides other than uranium, in order to assess its applicability in the 5f series. It is found to have excellent correlation with NBO and QTAIM covalency metrics, making it a promising addition to the computational toolkit for analysing metal-ligand bonding. Our range of metrics agree that the actinide-oxygen bonds are the most covalent of the elements studied, with those of the heavier group 4 elements the least. Within the early actinide series, Th stands apart from the other three elements considered, being consistently the least covalent.
V
XC
(M,O): the exchange-correlation metric quantifies covalency between M and O atomic basins in M(OC
6
H
5
)
4
(M = Ti, Zr, Hf, Ce, Th, Pa, U, Np).
Covalency is complex yet central to our understanding of chemical bonding, particularly in the actinide series. Here we assess covalency in a series of isostructural d and f transition element ...compounds M(OC
6
H
5
)
4
(M = Ti, Zr, Hf, Ce, Th, Pa, U, Np) using scalar relativistic hybrid density functional theory in conjunction with the Natural Bond Orbital (NBO), quantum theory of atoms in molecules (QTAIM) and interacting quantum atoms (IQA) approaches. The IQA exchange–correlation covalency metric is evaluated for the first time for actinides other than uranium, in order to assess its applicability in the 5f series. It is found to have excellent correlation with NBO and QTAIM covalency metrics, making it a promising addition to the computational toolkit for analysing metal–ligand bonding. Our range of metrics agree that the actinide-oxygen bonds are the most covalent of the elements studied, with those of the heavier group 4 elements the least. Within the early actinide series, Th stands apart from the other three elements considered, being consistently the least covalent.
The chemistry of the tris-carbene anion phenyltris(3-alkyl-imidazoline-2-yliden-1-yl)borate,
C3
Me
−
ligand, is initiated for f-block metal cations. Neutral, molecular complexes of the form
Ln(C3)
2
...I
are formed for cerium(
iii
), while a separated ion pair
Ln(C3)
2
I
forms for ytterbium(
iii
). DFT/QTAIM computational analyses of the complexes and related tridentate tris(pyrazolyl)borate (
Tp
) - supported analogs demonstrates the anticipated strength of the σ donation and confirms greater covalency in the metal-carbon bonds of the
C3
Me
−
complexes in comparison with those in the
Tp
Me,Me
complexes. The DFT calculations demonstrate the crucial role of THF solvent in accurately reproducing the contrasting molecular and ion-pair geometries observed experimentally for the Ce and Yb complexes.
The chemistry of the tris-carbene anion phenyltris(3-alkyl-imidazoline-2-yliden-1-yl)borate,
C3
Me
−
ligand, is initiated in the f-block.
A series of compounds M(OC6H5)4 (M = Ti, Zr, Hf, Ce, Th, U) is studied with hybrid density functional theory, to assess M-O bond covalency. The series allows for the comparison of d and f element ...compounds that are structurally similar. Two well-established analysis methods are employed: Natural Bond Orbital and the Quantum Theory of Atoms in Molecules. A consistent pattern emerges; the U-O bond is the most covalent, followed by Ce-O and Th-O, with those involving the heavier transition metals the least so. The covalency of the Ti-O bond differs relative to Ce-O and Th-O, with the orbital-based method showing greater relative covalency for Ti than the electron density-based methods. The deformation energy of r(M-O) correlates with the d orbital contribution from the metal to the M-O bond, while no such correlation is found for the f orbital component. f orbital involvement in M-O bonding is an important component of covalency, facilitating orbital overlap and allowing for greater expansion of the electrons, thus lowering their kinetic energy.
Four‐membered rings with a P2BCh core (Ch=S, Se) have been synthesized by the reaction of phosphinidene chalcogenide (Ar*P=Ch) and phosphaborene (Mes*P=BNR2). The mechanistic pathways towards these ...rings are explained by detailed computational work that confirmed the preference for the formation of P−P, not P−B, bonded systems, which seems counterintuitive given that both phosphorus atoms contain bulky ligands. The reactivity of the newly synthesized heterocycles, as well as that of the known (RPCh)n rings (n=2, 3), was probed by the addition of N‐heterocyclic carbenes, which revealed that all investigated compounds can act as sources of low‐coordinate phosphorus species.
Some serious (P2)BS: The combination of a phosphinidene chalcogenide and phosphaborene has created a unique heterocycle containing Group 13, 15, and 16 elements. Detailed theoretical work describes the likely pathway in generating P2BCh heterocycles. The reactivity of these, and other (RPCh)n rings, with N‐heterocyclic carbenes is reported.
Four-membered rings with a P
BCh core (Ch=S, Se) have been synthesized by the reaction of phosphinidene chalcogenide (Ar*P=Ch) and phosphaborene (Mes*P=BNR
). The mechanistic pathways towards these ...rings are explained by detailed computational work that confirmed the preference for the formation of P-P, not P-B, bonded systems, which seems counterintuitive given that both phosphorus atoms contain bulky ligands. The reactivity of the newly synthesized heterocycles, as well as that of the known (RPCh)
rings (n=2, 3), was probed by the addition of N-heterocyclic carbenes, which revealed that all investigated compounds can act as sources of low-coordinate phosphorus species.
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