Synthesis and Chloride Affinity of Sterically Demanding Ditopic Lithium Bis(pyrazol‐1‐yl)borates

Abstract

The synthesis and full characterization of the sterically demanding ditopic lithium bis(pyrazol‐1‐yl)borates Li2[p‐C6H4(B(Ph)pzR2)2] is reported (pzR = 3‐phenylpyrazol‐1‐yl (3Ph), 3‐t‐butylpyrazol‐1‐yl (3tBu)). Compound 3Ph crystallizes from THF as THF‐adduct 3Ph(THF)4 which features a straight conformation with a long Li···Li distance of 12.68(1) Å. Compound 3tBu was found to function as efficient and selective scavenger of chloride ions. In the presence of LiCl it forms anionic complexes [3tBuCl]− with a central Li‐Cl‐Li core (Li···Li = 3.75(1) Å).

Synthesis and Properties of Poly(pyrazolyl)borate and Related Boron-Centered Scorpionate Ligands. Part A: Pyrazole-Based Systems

“…(10) generally stops at the di-substitution stage. Polytopic poly(pyrazol-1-yl)borate ligands have shown great potential for the preparation of coordination polymers [107][108][109], multiple-decker sandwich complexes [110][111][112][113], metallomacrocycles [114], dinuclear complexes with cooperating metal ions [115][116][117][118], and metalloenzyme models [119]. As with the KBH 4 reaction, the pyrazole 3(5)-substituent ends up in the 3-position.…”

“…Recently Wagner et al [118] described the synthesis and full characterization of the ditopic lithium bis(pyrazol-1-yl)borates Li 2 [p-C 6 H 4 [B(Ph)(pz R ) 2 ] 2 ] (pz R = 3-phenylpyrazol-1-yl or 3-tbutylpyrazol-1-yl) and they reported unexpected differences in the affinity of their lithium salts towards chloride ions (Fig. 13).…”

RhI-complexes of ditopic bis(pyrazol-1-yl)borate ligands: Assessment of their catalytic activity towards phenylacetylene polymerization

“…The 3-phenylpyrazolyl-substituted scorpionate 4 is already known in the literature [24]. Its partially fluorinated congener 4 F was synthesized similar to 4 employing the aminoborane 3 [20] and 2 equivalents of a 1:1 mixture of Kpz Ph and Hpz Ph (Scheme 2).…”

“…Elemental analyses were performed by the microanalytical laboratory of the Goethe-University Frankfurt, Germany. Compounds 1 [40], 1 F [20], 3 [20], and 4 [24] were synthesized according to published procedures.…”

“…Our group has a long-standing interest in the development of oligotopic poly(pyrazol-1-yl)borate (''scorpionate" [12,13]) ligands [14][15][16][17][18][19][20] that are able to bring two metal ions into sufficiently close proximity so that they can act simultaneously on the same substrate molecule [21][22][23][24][25]. To identify promising applications of ditopic scorpionates of the general formula ½1; 4-ðBðR 0 Þpz R 2 Þ-C 6 H 4 -ðBðR 0 Þpz R 2 Þ 2À (pz R : 3-substituted pyrazolide) in homogeneous catalysis we chose to investigate the Rh-mediated polymerization of phenylacetylene, because (i) mononuclear complexes ½ðHBðR 0 Þpz R;R 2 ÞRhðcodÞ (cod: cyclooctadiene) reveal a high activity in this reaction [26], (ii) some benefit of two cooperating metal centers has already been confirmed for homogeneous olefin polymerization [27][28][29][30][31], and (iii) stereoregular poly(phenylacetylene) derivatives possess interesting and useful optoelectronic properties [32][33][34][35][36][37][38].…”