Di- and Tritopic Poly(pyrazol-1-yl)borate Ligands: Synthesis, Characterization, and Reactivity toward [Mn(CO)₅Br]

Abstract

Treatment of the ditopic phenylene-bridged bis(pyrazol-1-yl)borate K2[m-C6H4(B(tBu)pz2)2] (m-1) with [Mn(CO)5Br] results in ligand degradation with formation of the pyrazabole-bridged macrocyclic dimer {m-C6H4(B(tBu)pz)2}2 (2) and the triply pyrazolide-bridged dinuclear complex K[(OC)3Mn(μ-pz)3Mn(CO)3] (3). Even though the Ph-substituted scorpionate ligands Li2[m-C6H4(B(Ph)pz2)2] and Li2[p-C6H4(B(Ph)pz2)2] (m-5, p-5) possess a significantly higher hydrolytic stability than m-1, their reaction with [Mn(CO)5Br] also leads to B−N bond cleavage and gives the 3-type complex Li[(OC)3Mn(μ-pz)2(μ-Br)Mn(CO)3] (6). When, however, the corresponding tris(pyrazol-1-yl)borate ligands Li2[m-C6H4(Bpz3)2] and Li2[p-C6H4(Bpz3)2] (m-8, p-8) are employed, the clean formation of dinuclear Mn(CO)3 complexes Li2[m-C6H4(Bpz3Mn(CO)3)2] and Li2[p-C6H4(Bpz3Mn(CO)3)2] (m-11, p-11) is observed. The same is true for the novel tritopic scorpionate Li3[1,3,5-C6H3(Bpz3)3] (10), which gives ready access to the trinuclear Mn(CO)3 complex [1,3,5-C6H3(Bpz3Mn(CO)3)3] (12).

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

“…These results are remarkable in the light of the successful synthesis of 2 and 2 F and given the background that the compound ½ðHBpz Ph;Me 3 ÞRhðcodÞ, in which a scorpionate ligand with 3-phenyl-5-methylpyrazolyl substituents coordinates to the Rh I -ion in a j 2 -mode, is also readily accessible [41]. We attribute our failure to prepare Rh I -complexes of 4 and 4 F to the facts that bis(pyrazol-1-yl)borate ligands tend to have a lower stability than tris(pyrazol-1-yl)borates [40] and that sterically encumbered poly(pyrazol-1-yl)borates are generally more prone to B-N bond cleavage than less bulky derivatives [13,42].…”

“…2 and 2 F are available in high yield from the reaction of the bis(pyrazol-1-yl)borates 1 [40] and 1 F [20] with Rh 2 Cl 2 (cod) 2 (Scheme 1).…”

“…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.…”

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

“…The product was converted to the oligotopic poly(pyrazol-1-yl)borate by treatment with pyrazole/sodium pyrazolide (Fig. The first tritopic tris(pyrazol-1-yl)borate has been reported by Morawitz et al [124] which is a promising building block for the generation of two-dimensional transition metal aggregates (Fig. Fig.…”

Synthesis and Structural Characterization of the Tetrakis(methimazolyl)borates Li[Bmt4] and [Ru(p‐cymene)(Bmt4)][PF6]

“…In previous studies we had described the synthesis and structural characterization of several di-and tritopic ligands with a phenylene linker 4, 5, 6, and 7, as shown in Figure 2 [7,8,9,10]. Now we are interested in mononuclear soft ligand systems with binding modes A and B, as depicted in Figure 1.…”