Unusual Cage Rearrangements in 10-Vertex nido-5,6-Dicarbaborane Derivatives: An Interplay between Theory and Experiment

Abstract

The reaction between selected X-nido-5,6-CBH compounds (where X = Cl, Br, I) and "Proton Sponge" [PS; 1,8-bis(dimethylamino)naphthalene], followed by acidification, results in extensive rearrangement of all cage vertices. Specifically, deprotonation of 7-X-5,6-CBH compounds with one equivalent of PS in hexane or CHCl at ambient temperature led to a 7 → 10 halogen rearrangement, forming a series of PSH[10-X-5,6-CBH] salts. Reprotonation using concentrated HSO in CHCl generates a series of neutral carbaboranes 10-X-5,6-CBH, with the overall 7 → 10 conversion being 75%, 95%, and 100% for X = Cl, Br, and I, respectively. Under similar conditions, 4-Cl-5,6-CBH gave ∼66% conversion to 3-Cl-5,6-CBH. Since these rearrangements could not be rationalized using the B-vertex swing mechanism, new cage rearrangement mechanisms, which are substantiated using DFT calculations, have been proposed. Experimental B NMR chemical shifts are well reproduced by the computations; as expected δ(B) for B(10) atoms in derivatives with X = Br and I are heavily affected by spin-orbit coupling.

Various types of non-covalent interactions contributing towards crystal packing of halogenated diphospha-dicarbaborane with an open pentagonal belt

“…The discrepancy between the calculated and experimental chemical shift results from the neglect of the effect of spin-orbit (SO) coupling on the overall shielding, which is not taken into account in the GIAO-MP2 scheme. However, it has been shown that due to iodine being terminally bonded to a boron atom within a neutral boron cluster, SO coupling increases the contribution of this B atom towards overall shielding by about 20 ppm, 7,8 which would considerably improve the fit in the present case.…”

Various types of non-covalent interactions contributing towards crystal packing of halogenated diphospha-dicarbaborane with an open pentagonal belt

“…The discrepancy between the calculated and experimental chemical shift results from the neglect of the effect of spin-orbit (SO) coupling on the overall shielding, which is not taken into account in the GIAO-MP2 scheme. However, it has been shown that due to iodine being terminally bonded to a boron atom within a neutral boron cluster, SO coupling increases the contribution of this B atom towards overall shielding by about 20 ppm, 7,8 which would considerably improve the fit in the present case.…”

Reactions of Experimentally Known Closo-C2B8H10 with Bases. A Computational Study

“…All of the stationary points in the reactions of closo-1,2-, 1,6-, and 1,10-C 2 B 8 H 10 with OH (−) were optimized and frequencies were calculated at the SMD(water) [15,16]/B3LYP/6-311+G(2d,p) level, a model chemistry well-established for this class of materials [4][5][6]. The entries in Table 1 for B3LYP/6-311+G(2d,p) are single-point energies at SMD(water)/B3LYP/6-311+G(2d,p)-optimized geometries.…”

“…This significant geometrical change initiates a continuation of the reaction through other four subsequent TSs to the next known isomer, i.e., oP4-N. The reaction of the 1,6-isomers (see Figures S5 and S6) was a result of the simultaneous initial attack of NH 3 on B(3) and C (6); the N atom forms a cap above the B(2)B(3)C(6) triangle in the transition state with a free energy barrier of 34.6 kcal•mol −1 . The second free energy barrier was even higher, 52.0 kcal•mol −1 and might account for the fact that this reaction does not occur experimentally.…”

A simple and high-yield route to iridium, rhodium, osmium and ruthenium nido -6-metalladecaborane compounds

“…Therefore, the formation of 6 implies a rearrangement of the initial 10-vertex anion or some other intermediate. Given the fact that we have characterized 7 as a nido-5-osamadecaborane, it is reasonable to propose that the nido-6-osmadecaborane anion may undergo a vertex-swing, 47,[66][67][68][69] as illustrated in Scheme 4 C, which transforms the metal centre from a vertex coordinated to three boron units into an osmium centre linked to four boron vertices. This hypothetical nido-5-anion could substitute the chlorine ligands of the platinum complex and liberate a proton to finally form 6, which exhibits the metal centres apart, forming the pentagonal face of the 11-vertex cluster.…”

Various types of non-covalent interactions contributing towards crystal packing of halogenated diphospha-dicarbaborane with an open pentagonal belt

“…The discrepancy between the calculated and experimental chemical shift results from the neglect of the effect of spin-orbit (SO) coupling on the overall shielding, which is not taken into account in the GIAO-MP2 scheme. However, it has been shown that due to iodine being terminally bonded to a boron atom within a neutral boron cluster, SO coupling increases the contribution of this B atom towards overall shielding by about 20 ppm, 7,8 which would considerably improve the fit in the present case.…”

Reactions of Experimentally Known Closo-C2B8H10 with Bases. A Computational Study

“…All of the stationary points in the reactions of closo-1,2-, 1,6-, and 1,10-C 2 B 8 H 10 with OH (−) were optimized and frequencies were calculated at the SMD(water) [15,16]/B3LYP/6-311+G(2d,p) level, a model chemistry well-established for this class of materials [4][5][6]. The entries in Table 1 for B3LYP/6-311+G(2d,p) are single-point energies at SMD(water)/B3LYP/6-311+G(2d,p)-optimized geometries.…”

“…This significant geometrical change initiates a continuation of the reaction through other four subsequent TSs to the next known isomer, i.e., oP4-N. The reaction of the 1,6-isomers (see Figures S5 and S6) was a result of the simultaneous initial attack of NH 3 on B(3) and C (6); the N atom forms a cap above the B(2)B(3)C(6) triangle in the transition state with a free energy barrier of 34.6 kcal•mol −1 . The second free energy barrier was even higher, 52.0 kcal•mol −1 and might account for the fact that this reaction does not occur experimentally.…”

A simple and high-yield route to iridium, rhodium, osmium and ruthenium nido -6-metalladecaborane compounds

“…Therefore, the formation of 6 implies a rearrangement of the initial 10-vertex anion or some other intermediate. Given the fact that we have characterized 7 as a nido-5-osamadecaborane, it is reasonable to propose that the nido-6-osmadecaborane anion may undergo a vertex-swing, 47,[66][67][68][69] as illustrated in Scheme 4 C, which transforms the metal centre from a vertex coordinated to three boron units into an osmium centre linked to four boron vertices. This hypothetical nido-5-anion could substitute the chlorine ligands of the platinum complex and liberate a proton to finally form 6, which exhibits the metal centres apart, forming the pentagonal face of the 11-vertex cluster.…”

Various types of non-covalent interactions contributing towards crystal packing of halogenated diphospha-dicarbaborane with an open pentagonal belt

“…The discrepancy between the calculated and experimental chemical shift results from the neglect of the effect of spin-orbit (SO) coupling on the overall shielding, which is not taken into account in the GIAO-MP2 scheme. However, it has been shown that due to iodine being terminally bonded to a boron atom within a neutral boron cluster, SO coupling increases the contribution of this B atom towards overall shielding by about 20 ppm, 7,8 which would considerably improve the fit in the present case.…”

Reactions of Experimentally Known Closo-C2B8H10 with Bases. A Computational Study

“…All of the stationary points in the reactions of closo-1,2-, 1,6-, and 1,10-C 2 B 8 H 10 with OH (−) were optimized and frequencies were calculated at the SMD(water) [15,16]/B3LYP/6-311+G(2d,p) level, a model chemistry well-established for this class of materials [4][5][6]. The entries in Table 1 for B3LYP/6-311+G(2d,p) are single-point energies at SMD(water)/B3LYP/6-311+G(2d,p)-optimized geometries.…”

“…This significant geometrical change initiates a continuation of the reaction through other four subsequent TSs to the next known isomer, i.e., oP4-N. The reaction of the 1,6-isomers (see Figures S5 and S6) was a result of the simultaneous initial attack of NH 3 on B(3) and C (6); the N atom forms a cap above the B(2)B(3)C(6) triangle in the transition state with a free energy barrier of 34.6 kcal•mol −1 . The second free energy barrier was even higher, 52.0 kcal•mol −1 and might account for the fact that this reaction does not occur experimentally.…”

A simple and high-yield route to iridium, rhodium, osmium and ruthenium nido -6-metalladecaborane compounds

“…Therefore, the formation of 6 implies a rearrangement of the initial 10-vertex anion or some other intermediate. Given the fact that we have characterized 7 as a nido-5-osamadecaborane, it is reasonable to propose that the nido-6-osmadecaborane anion may undergo a vertex-swing, 47,[66][67][68][69] as illustrated in Scheme 4 C, which transforms the metal centre from a vertex coordinated to three boron units into an osmium centre linked to four boron vertices. This hypothetical nido-5-anion could substitute the chlorine ligands of the platinum complex and liberate a proton to finally form 6, which exhibits the metal centres apart, forming the pentagonal face of the 11-vertex cluster.…”