Search

The photolytic or oxidative liberation of a cyclic (amino)(alkyl)carbene (CAAC)-stabilized arylborylene in the presence of organoazides yielded borylene-organoazide complexes (4a,b) has been achieved in a manner akin to the first step of the Staudinger reaction. Similarly, a CAAC-stabilized aminoborylene also afforded borylene-organoazide complexes (6a–c), which further undergo rearrangement to produce aminoborane triazene species (7a,b). [ABSTRACT FROM AUTHOR]

Although Lipscomb predicted in 1977 that supra-icosahedral boron clusters would be viable, their synthesis has been impeded by the unavailability of appropriate synthetic methodologies. Herein, we report the first examples of the open 16-vertex oblato–hypho-titanaborane clusters [(Cp*Ti)2B14H17R] (1: R = H; 2: R = Me) having a non-Wadean 19-skeletal-electron-pair count. Interestingly, these clusters show a six-membered [Ti2B4] open face, which could lead to closo-19-vertex clusters. [ABSTRACT FROM AUTHOR]

Although Lipscomb predicted in 1977 that supra-icosahedral boron clusters would be viable, their synthesis has been impeded by the unavailability of appropriate synthetic methodologies. Herein, we report the first examples of the open 16-vertex oblato–hypho-titanaborane clusters [(Cp*Ti)2B14H17R] (1: R = H; 2: R = Me) having a non-Wadean 19-skeletal-electron-pair count. Interestingly, these clusters show a six-membered [Ti2B4] open face, which could lead to closo-19-vertex clusters. [ABSTRACT FROM AUTHOR]

Isolation of planar [B6H6] is a long‐awaited goal in boron chemistry. Several attempts in the past to stabilize [B6H6] were unsuccessful due to the domination of polyhedral geometries. Herein, we report the synthesis of a triple‐decker sandwich complex of titanium [(Cp*Ti)2(μ‐η6 : η6‐B6H6)(μ‐H)6] (1), which features the first‐ever experimentally achieved nearly planar six‐membered [B6H6] ring, albeit within a [B6H12] borate. The small deviation from planarity is a direct consequence of the predicted structural pattern of the middle ring in 24 Valence Electron Count (VEC) triple‐decker complexes. The large ring size of [B6H6] in 1 brings the metal–metal distance into the bonding range. However, significant electron delocalization from the M−M bonding orbital to the bridging hydrogen and B−B skeleton in the middle decreases its bond strength. [ABSTRACT FROM AUTHOR]

Isolation of planar [B6H6] is a long‐awaited goal in boron chemistry. Several attempts in the past to stabilize [B6H6] were unsuccessful due to the domination of polyhedral geometries. Herein, we report the synthesis of a triple‐decker sandwich complex of titanium [(Cp*Ti)2(μ‐η6 : η6‐B6H6)(μ‐H)6] (1), which features the first‐ever experimentally achieved nearly planar six‐membered [B6H6] ring, albeit within a [B6H12] borate. The small deviation from planarity is a direct consequence of the predicted structural pattern of the middle ring in 24 Valence Electron Count (VEC) triple‐decker complexes. The large ring size of [B6H6] in 1 brings the metal–metal distance into the bonding range. However, significant electron delocalization from the M−M bonding orbital to the bridging hydrogen and B−B skeleton in the middle decreases its bond strength. [ABSTRACT FROM AUTHOR]

Isolation of planar [B6H6] is a long‐awaited goal in boron chemistry. Several attempts in the past to stabilize [B6H6] were unsuccessful due to the domination of polyhedral geometries. Herein, we report the synthesis of a triple‐decker sandwich complex of titanium [(Cp*Ti)2(μ‐η6 : η6‐B6H6)(μ‐H)6] (1), which features the first‐ever experimentally achieved nearly planar six‐membered [B6H6] ring, albeit within a [B6H12] borate. The small deviation from planarity is a direct consequence of the predicted structural pattern of the middle ring in 24 Valence Electron Count (VEC) triple‐decker complexes. The large ring size of [B6H6] in 1 brings the metal–metal distance into the bonding range. However, significant electron delocalization from the M−M bonding orbital to the bridging hydrogen and B−B skeleton in the middle decreases its bond strength. [ABSTRACT FROM AUTHOR]

Isolation of planar [B6H6] is a long‐awaited goal in boron chemistry. Several attempts in the past to stabilize [B6H6] were unsuccessful due to the domination of polyhedral geometries. Herein, we report the synthesis of a triple‐decker sandwich complex of titanium [(Cp*Ti)2(μ‐η6 : η6‐B6H6)(μ‐H)6] (1), which features the first‐ever experimentally achieved nearly planar six‐membered [B6H6] ring, albeit within a [B6H12] borate. The small deviation from planarity is a direct consequence of the predicted structural pattern of the middle ring in 24 Valence Electron Count (VEC) triple‐decker complexes. The large ring size of [B6H6] in 1 brings the metal–metal distance into the bonding range. However, significant electron delocalization from the M−M bonding orbital to the bridging hydrogen and B−B skeleton in the middle decreases its bond strength. [ABSTRACT FROM AUTHOR]

Despite the synthesis and structural characterization of closo‐hydroborate dianions, [BnHn]2− (n=6–12) more than 50 years ago, some ambiguity remains about the structure of [B8H8]2−. Although the solid‐state structure of [B8H8]2− was established by single‐crystal X‐ray studies in 1969, fast rearrangements in solution at accessible temperatures prevented its detailed characterization. We therefore stabilized a derivative of [B8H8]2− by using Cp2MBH3 and structurally characterized two new octaborane analogues, [(Cp2MBH3)2B8H6] (Cp=η5‐C5H5; M=Zr (1‐Zr) and Hf (1‐Hf)), so that the dynamics of the B8 skeleton were arrested. The solid‐state structures of both 1‐Zr and 1‐Hf comprise a dodecahedron core protected by {Cp2MBH3} moieties on both sides of the cluster. Spectroscopic characterization (11B NMR) validates the intactness of the B8 dodecahedron core in solution as well. Theoretical calculations establish that the two exo‐{Cp2MBH3} fragments provide structural and electronic structural stability to the B8 core and its intact dodecahedral dianionic nature. Furthermore, we propose isodesmic equations for the formation of higher analogues of the Bn core (n>8) guarded by different group 4 transition metals. Our analysis suggests that, as we move to higher polyhedra (n>10), the formation becomes unfavourable irrespective of metal. [ABSTRACT FROM AUTHOR]

Triply-bridging bis-{hydrido(borylene)} and bis-borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe2(CO)9] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl4] (Cp*=η5 -C5Me5) and [LiBH4·THF] afforded triply-bridging bis-{hydrido(borylene)}, [(μ3- BH)2H2{Cp*W(CO)2}2{Fe(CO)2}] (1) and bis-borylene, [(μ3- BH)2{Cp*W(CO)2}2{Fe(CO)3}] (2). The chemical bonding analyses of 1 show that the B H interactions in bis-{hydrido (borylene)} species is stronger as compared to the M H ones. Frontier molecular orbital analysis shows a significantly larger energy gap between the HOMO-LUMO for 2 as compared to 1. In an attempt to synthesize the ruthenium analogue of 1, a similar reaction has been performed with [Ru3(CO)12]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(μ3- BH)2{WCp*(CO)2}2{Ru(CO)3}] (2’), an analogue of 2. In search for the isolation of bridging bis-borylene species of Rh, we have treated [Co2(CO)8] with nido-[(RhCp*)2(B3H7)], which afforded triply-bridging bis-borylene species [(μ3- BH)2(RhCp*)2Co2(CO)4(μ-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; ¹ H, 11B, 13C NMR spectroscopy; IR spectroscopy and mass spectromet [ABSTRACT FROM AUTHOR]

The room‐temperature reaction of [Cp*TaCl4] with LiBH4⋅THF followed by addition of S2CPPh3 results in pentahydridodiborate species [(Cp*Ta)2(μ,η2:η2‐B2H5)(μ‐H)(κ2,μ‐S2CH2)2] (1), a classical [B2H5]− ion stabilized by the binuclear tantalum template. Theoretical studies and bonding analysis established that the unusual stability of [B2H5]− in 1 is mainly due to the stabilization of sp2‐B center by electron donation from tantalum. Reactions to replace the hydrogens attached to the diborane moiety in 1 with a 2 e {M(CO)4} fragment (M=Mo or W) resulted in simple adducts, [{(Cp*Ta)(CH2S2)}2(B2H5)(H){M(CO)3}] (6: M=Mo and 7: M=W), that retained the diborane(5) unit. [ABSTRACT FROM AUTHOR]

In an effort to isolate the chalcogen-rich niobium analogue of [(Cp*Ta)3(μ-S)3(μ3-S)3BH], the room temperature reaction of [Cp*NbCl4] (Cp* = η5-C5Me5) with Li[BH2S3] was carried out. Although the objective of isolating the niobium analogue was not achieved, the reaction yielded a homocubane-type cluster [(Cp*Nb)3(μ-S)3(μ3-S)3(μ-S)BH], 1, and a hexa-sulfido cluster [(Cp*Nb)3(μ-S)6], 2. Cluster 1 is a notable example of a homocubane-type cluster in which one of the vertices of the homocubane is missing. Compound 1 may be considered as a hypo-electronic cluster with an electron count of 64 cve (cve = cluster valence electrons), whereas compound 2 shows the presence of two doubly bridging η1-S around each Nb–Nb bond. On the other hand, the room temperature reaction of [Cp*TaCl4] with selenaborate ligand, [LiBH2Se3], led to the formation of [(Cp*Ta)3(μ-Se)4{μ-Se2(Se2)}], 3. Compound 3 is one of the rarest examples having a Ta3Se6 core structure with a unique diselenide bridging fragment. The presence of a short Se–Se bond of this diselenide unit makes this molecule of further interest. All these compounds were characterized by 1H, 11B{1H} and 13C{1H} NMR spectroscopy, infrared spectroscopy, mass spectrometry, and single-crystal X-ray crystallography. Density functional theory (DFT) calculations were carried out to provide insight into the bonding and electronic structures of these chalcogen-rich trimetallic clusters. [ABSTRACT FROM AUTHOR]