Hydrotris(indazolyl)borates:  Homoscorpionates with Tunable Regiochemistry

Abstract

A series of hydrotris(indazolyl)borates containing diverse substituents on the indazole ring and representing two types of regiochemistries have been synthesized. Indazoles with a 7-alkyl substituent or a 6,7-fused benzo ring formed ligands with boron bonded to the less hindered N-2 ()Tp 3Bo ), while those with alkyl or aryl substituents in any other position yielded ligands with boron bonded to the more hindered N-1 ()Tp 4Bo ), thus being the first example of homoscorpionates with 4,5-substituents. Octahedral homo-and heteroleptic complexes of Co, Fe, and Zn have been prepared and characterized, as well as complexes of the typesand [Rh(L)(CO) 2 ]. X-ray crystallography provided structures of the complexes [Rh(HB{3-methylindazol-1-yl} 3 )(COD)], 1 (space group P2 1 /n; a ) 11.766(2), b ) 16.189(2), c ) 15.149(2) Å; β ) 92.51(1)°; Z ) 4; R ) 0.0306 for 4318 independent reflections), [Co(HB{7-methylinazol-2-yl} 3 )(HB{3neopentylpyrazol-1-yl} 3 )], 2 (space group P1 h; a ) 13.368(4), b ) 13.652(4), c ) 16.203(9) Å; R ) 73.73(4), β) 71.26(3), γ ) 63.54(2)°; Z ) 2; R ) 0.0761 for 7721 independent reflections), and indazol-2-yl}borate)(hydrotris{3-neopentylpyrazol-1-yl}borate)]‚C 6 H 5 CN, 3 (space group P1 h; a ) 13.216(6), b ) 13.706(4), c ) 17.881(6) Å; R ) 73.79(2), β ) 86.71(3), γ ) 85.61(3)°; Z ) 2; R ) 0.1138 for 6698 independent reflections).

Synthesis of New Tripodal Tri‐Functionalized Hydrotris(indazol‐1‐yl)borate Ligands and X‐ray Structures of Their Cyclopentadieneruthenium Complexes

“…Potassium hydrotris(indazol-1-yl)borate (KTp 4Bo ) was prepared according to a literature procedure. [10] NMR spectra were recorded with Bruker AM 250 or Avance 500 spectrometers and full assignments were made using COSY, ROESY, HMBC, and HMQC methods when necessary. The numbering scheme for the indazol derivatives is given in molecule 3 (see Scheme 1 and Scheme 2).…”

“…Concerning the regiochemistry of the reaction, Trofimenko has shown on the hydrotris(indazol-1-yl)borate ligand [10] that the interplay of steric and electronic factors tilts in favor of the latter, giving a product that is sterically hindered around the boron atom but not on the coordination side. Similarly, we obtained exclusively the product resulting from the fusion of the benzo ring at the 4-5-position (giving the Tp 4Bo product) in which the boron atom is bound to the more hindered nitrogen atom and no trace of the 3-4 fusion product (Tp 3Bo ).…”

“…However its analogue, hydrotris(indazolyl)borate (Tp 4Bo ), has not stimulated intense studies since its synthesis in 1995. [10] Nevertheless tris(indazolyl)borate bears two advantages over trispyrazolylborate. First it is larger, but the increase in size is not accompanied by a decrease in the rigidity of the molecule.…”

Hydrotris(1,2,4-triazolyl)borato Complexes with the Main Group Elements Ca, Sr, and Pb - Unexpectedly Bent ML2 Structures and a Stereochemically Inactive Lone Pair at Lead(II)

“…Towards lead(II) this interest is closely related to the stereochemical activity or nonactivity of the`lone pair' of electrons on the metal atom [10]. For example, in PbTp 2 the lone pair was found to be stereochemically active, while with the more bulky ligand in PbTp* 2 , i. e. PbTp Me2 Particular attention is sometimes devoted to special azolyl rings, such as triazolyl [13±16], tetrazolyl [17], 3,5-bis(trifluoromethyl)pyrazolyl [18], and indazolyl [19,20]. These ligands can exert quite different electronic and structural effects when compared with the Tp analog [15,21].…”

The chemistry of 1,2,3,4,5-pentaphenylcyclopentadienyl hydrotris(indazolyl)borate ruthenium(II) complexes, building blocks for the construction of potential organometallic molecular motors

“…The bromine is substituted by 1 -cyclopentadiene, then a thermal decarbonylation yields the pentaphenylferrocene. Similarly, the synthesis of complex 7 was realized by a direct substitution of the carbonyl and bromine ligands of 5 by the scorpionate ligand hydrotris(indazolyl)borate [31] (Scheme 3).…”