Difunctional Pyrazole Derivatives − Key Compounds en Route to Multidentate Pyrazolate Ligands

Abstract

Straightforward syntheses for some basic functional pyrazole derivatives are reported. These compounds serve as starting materials for the preparation of a series of new 3,5-donorsubstituted multifunctional pyrazole compounds, which may act as compartmental dinucleating ligand scaffolds for the controlled assembly of bimetallic complexes. The thp-protected 3,5-bis(chloromethyl)pyrazole (1), and in particular the more reactive 3,5-bis(bromomethyl) analogue 3, permit efficient attachment of various N-donor side arms through nucleophilic substitution reactions. The preparation of the enantiomerically pure (methoxymethyl)pyrrolidine derivative 2e by this route makes use of the intrinsic C 2 symmetry of the pyrazole-based framework, and a dizinc complex [a]

Synthesis and structural characterization of (CH2)n-bridged indenyl-pyrazoles and their cyclopentadienyl nickel(II) complexes

“…NHC-(CH 2 ) n -functionalized fluorenyl complexes of metals have also been known [21]. Nitrogen or other heteroatom-donor side chain-functionalized pyrazolates can serve as polydentate ligands, and a pyrazol-1-yl tethered to a Cp ligand might also serve as an intramolecular function as a chelate donor in metal complexes [23][24][25][26]. Bis(cyclopentadienyl)-fuctionalized pyrazoles (H 3 L), i.e., 3,5-bis(fluoren-9-ylmethyl)-1H-pyrazole and 3,5-bis(inden-3-ylmethyl)-1H-pyrazole, and their lithium salts (Li 3 L) were synthesized [27] (Chart 1).…”

“…However, in our cases, reactions of nickelocene with 7, 8, 13, 16 or 18 under mild (room temperature) or relatively harsh (in refluxing toluene) conditions only yielded trimetallic complexes of type [CpNi{4-(Ind-(CH 2 ) n )-RR 0 Pz} 2 ] 2 Ni (20)(21)(22)(23)(24) These results are attributed to the bulkier hindrance of the 3,5-diphenyl groups on the pyrazolyl ring of 19 than that of the Pz-3,5-disubstituents in other indenyl-pyrazoles. Attempt to prepare and isolate the desired product analogous to complexes 20-24 or 25 from the reaction of Cp 2 Ni and 14 was unsuccessful.…”

“…: 154°C. 1 (20)(21)(22)(23)(24) and [CpNi{Ind-(CH 2 ) 3 -Pz}] 2 (25) -a general procedure A mixture of nickelocene (Cp 2 Ni) and an indenyl-pyrazole in 1:1 molar ratio was stirred in refluxing toluene, forming a deep-red solution. All the volatiles were removed under reduced pressure and the resultant residue was extracted with toluene, filtered through a short pad of celite.…”

Efficient Syntheses of Some Versatile 3,5-Bifunctional Pyrazole Building Blocks

“…These should be amenable via high-yielding and straightforward syntheses, which is particularly true for N-unsubstituted pyrazoles. 7,8 Established pyrazole building blocks include dialdehyde A 9 and diacid dichloride B 10 as well as diester C 11 (Figure1), all of which have proven useful for the preparation of, for example, macrocycles and multidentate ligand scaffolds incorporating one or more pyrazole moieties. 3 In order to broaden the scope of these systems, we set out to develop efficient syntheses for a variety of new 1H-pyrazole derivatives related to A-C with carbonyl or ester groups in the 3-and 5-positions, but with different substitution pattern both at the pyrazole-C4 position and the side arm carbonyl functions.…”

Bifunktionelle Cp∩N-Komplexe: ungewöhnliche Strukturen und elektronische Kommunikation in hochgradig präorganisierten Zweikernkomplexen

“…Die Einf¸hrung des Cp-Grundkˆrpers in die Seitenarme funktionalisierter Pyrazolderivate wie 1 [5] erwies sich als unerwartet schwierig. Zur Synthese wurde das πgesch¸tzte™ Cp-Derivat [CpMn(CO) 3 ] in einer [Pd(PPh 3 ) 2 ]/ZnCl 2 -katalysierten Kreuzkupplung [6] mit dem Pyrazolkern unter Bildung von 2 verkn¸pft (Schema 1).…”