Metal–Metal Distances at the Limit: Cr–Cr 1.73 Å – the Importance of the Ligand and its Fine Tuning

Noor, Awal; Glatz, Germund; Müller, Robert; Kaupp, Martin; Demeshko, Serhiy; Kempe, Rhett

doi:10.1002/zaac.200900175

Cited by 108 publications

(70 citation statements)

References 21 publications

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“…In 2005, Power et al [86] reported the synthesis of the first isolable formal quintuply bonded (σ 2 π 4 δ 4 ) dichromium complex ArCrCrAr (Ar = 2,6-(2,6-iPr 2 C 6 H 3 ) 2 C 6 H 3 ) with an unusually short Cr-Cr distance (1.835 Å). This report stimulated several theoretical and experimental studies [87][88][89][90][91][92][93][94][95] in which the nature of the Cr-Cr bond was probed. Since then, several complexes featuring ultra-short Cr-Cr bonds of around 1.75 Å have been identified [88][89][90][94][95][96].…”

Section: High Bond Orders In Transition Metalssupporting

confidence: 56%

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Strong Chemical Bonds

Notario

2016

Encyclopedia of Physical Organic Chemistry, 5 Volume Set

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Section: High Bond Orders In Transition Metalssupporting

confidence: 56%

“…Since then, several complexes featuring ultra-short Cr-Cr bonds of around 1.75 Å have been identified [88][89][90][94][95][96]. The shortest Cr-Cr distance (1.729 Å) to date has been observed by Noor et al [95].…”

Section: High Bond Orders In Transition Metalsmentioning

confidence: 97%

Strong Chemical Bonds

Notario

2016

Encyclopedia of Physical Organic Chemistry, 5 Volume Set

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“…[60,61] Even most of the recently described dinuclear chromium complexes with a quintuple bond follow, in principle, this concept of the stabilization of dinuclear complexes by L = ABC. [62][63][64] Sasols PNP ligands, [7] as typical L = ABC ligands, are the best for selective tetramerization but not totally exclusive. A very small number of exceptions exist with L = ABCD, giving some 1-octene selectivity like PNNP [7] and PCCP.…”

Section: Experimental Backgroundmentioning

confidence: 99%

An Alternative Mechanistic Concept for Homogeneous Selective Ethylene Oligomerization of Chromium‐Based Catalysts: Binuclear Metallacycles as a Reason for 1‐Octene Selectivity?

Peitz

Aluri

Peulecke

et al. 2010

Chemistry A European J

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An alternative concept for the selective catalytic formation of 1-octene from ethylene via dimeric catalytic centers is proposed. The selectivity of the tetramerization systems depends on the capability of ligands to form binuclear complexes that subsequently build up and couple two separate metallacyclopentanes to form 1-octene selectively. Comparison of existing catalytic processes, the ability of the bis(diarylphosphino)amine (PNP) ligand to bridge two metal centers, and the experimental background support the proposed binuclear mechanism for ethylene tetramerization.

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“…We also made an effort to synthesize a com pound containing a Cr-Cr bond similar to diazadi ene and amidinate derivatives containing the chromi um-chromium quintuple bond synthesized recently. [34][35][36][37][38][39][40][41] Results and Discussion Synthesis and characterization of compounds 2, 4-8, and 10. The replacement of CO groups by dpp bian in chromium hexacarbonyl requires the presence of an ex cess of the latter (2-4 moles of dpp bian per mole of Cr(CO) 6 ), the prolonged heating of the reaction mixture (20 h at 80 C), and the removal from time to time of carbon monoxide that formed.…”

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“…Zr-C(38) 2.4802(19) N(1)-Zr-N(2) 87.94(6) Zr-C(39) 2.507(2) N(1)-Zr-Cl 109.53(4) Zr-C(40) 2.520(2) N(2)-Zr-Cl 113.90(4) Zr-C(41) 2.498(2)…”

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Compounds of chromium, titanium, and zirconium with different reduced forms of acenaphthene-1,2-diimine

et al. 2014

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The reaction of Cr(CO) 6 with 1,2 bis[(2,6 diisopropylphenyl)imino]acenaphthene (1, dpp bian) affords a chromium complex with the neutral diimine ligand (dpp bian)Cr(CO) 4 (2). The exchange reactions of the compound [(dpp bian)Cr( Cl)(THF)] 2 (3) with LiOH, PhCCNa, [(CH 3 ) 3 Si] 2 NK, C 5 H 5 Na, and C 5 Me 5 Na give the corresponding radical anion derivatives, viz., [(dpp bian)Cr( OH)] 2 (4), [(dpp bian)Cr( CCPh)] 2 (5), (dpp bian)Cr[N(SiMe 3 ) 2 ] (THF) (6), (dpp bian)Cr(C 5 H 5 ) (7), and (dpp bian)Cr(C 5 Me 5 ) (8). The titanium and zirconi um complexes with the acenaphthene 1,2 diimine dianion, viz., (dpp bian) 2 Ti (9) and (dpp bian)Zr(Cl)Cp (10), were synthesized by the reactions of Na 2 (dpp bian) with TiCl 4 and CpZrCl 3 , respectively. All compounds were characterized by IR spectroscopy and elemental analysis. Diamagnetic derivatives 2, 9, and 10 were additionally studied by 1 H NMR spectro scopy. The structures of products 2, 4-8, and 10 were determined by X ray diffraction.Key words: diimine ligands, transition metals, molecular and electronic structures.1,2 Bis(arylimino)acenaphthenes were put in use as ligands in the coordination chemistry about 10 years ago. 1,2 Bis[(2,6 diisopropylphenyl)imino]acenaphthene (1, dpp bian) is the most commonly applied ligand of this class. Its distinguishing features are, first, the conforma tional rigidity of the diimine moiety, the nitrogen atoms of which are coordinated to the metal atom, and, second, the shielding of the coordination area by bulky substituents at the nitrogen atoms. This ensures the formation of mono meric metal complexes, in which the diimine ligand never acts as a bridging ligand. The absolutely unique property of the dpp bian ligand is its ability to be reversibly reduced by alkali metals to mono , di , tri , and tetraanions to form the salts [(dpp bian) n-M + n (Et 2 O) m ] (M = Li, Na; n = 1-4, m = 1-4). 1,2 Organometallic compounds, for example, Me 2 Mg 3 or EtMgBr, 4 can also reduce dpp bian. In the former case, the reaction is accompanied by the elimination of the methyl radical to give the oragno magnesium derivative with the dpp bian radical anion [(dpp bian)MgMe] 2 . The reaction of dpp bian with a Grignard reagent affords the addition product of the oragnomagnesium compound at one of the C=N bonds of the diimine, (dpp bian Et)MgBr(Et 2 O) 2 . Both reactions proceed through the one electron transfer to form the dpp bian radical anion, which recombines with the ethyl radi cal to give the final product.A series of compounds containing unusual metal-met al bonds, including derivatives of Group 13 metals having unique reactivity toward alkynes, of the general formula (dpp bian)M-M(dpp bian) (M = Ga, Al) were synthe sized using dpp bian as the ligand. 5-9 Like other diimines, dpp bian can stabilize low oxidation states, including di valent states of silicon and germanium. 10-12 The redox isomerization in the complex of a 4f element, viz., in the compound [(dpp bian)YbBr(DME)] 2 , 13 was accom plished for the first time using the dpp b...

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Metal–Metal Distances at the Limit: Cr–Cr 1.73 Å – the Importance of the Ligand and its Fine Tuning

Cited by 108 publications

References 21 publications

Strong Chemical Bonds

Strong Chemical Bonds

An Alternative Mechanistic Concept for Homogeneous Selective Ethylene Oligomerization of Chromium‐Based Catalysts: Binuclear Metallacycles as a Reason for 1‐Octene Selectivity?

Compounds of chromium, titanium, and zirconium with different reduced forms of acenaphthene-1,2-diimine

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