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Synthesis and Characterization of a Novel Triangular Rh2au Cluster

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Synthesis and Characterization of a Novel Triangular Rh2au Cluster Full Papers ChemistryOpen doi.org/10.1002/open.202000217 1 2 3 Synthesis and Characterization of a Novel Triangular Rh2Au 4 5 Cluster Compound Inspired by the Isolobality Concept 6 [a] [a] [a] [b] 7 Hans-Christian Böttcher,* Marion Graf, Peter Mayer, and Manfred Scheer 8 Dedicated to Professor Paul Knochel on the occasion of his 65th birthday 9 10 5 5 11 The synthesis of [Rh2(η -Cp)2(μ-H)(μ-PPh2)2]BF4 (2) by protona- compound [Rh2{μ-Au(PPh3)}(η -Cp)2(μ-PPh2)2]BF4 (3) in good 5 12 tion reaction of the metal basic complex [Rh2(η -Cp)2(μ-PPh2)2] yield. Metal cluster salt 3 was fully characterized by spectro- 13 (1) with tetrafluoroboric acid in diethyl ether is described. scopic data and its molecular structure in the crystal was 14 Complex salt 2 was obtained in high yield and fully charac- determined by X-ray diffraction. The structural comparison of 15 terized by spectroscopic means and X-ray crystal diffraction. the protonated dirhodium core in the cationic complex of 2 16 Applying the isolobal analogy between H and the fragment Au with the Rh2Au framework in 3 is in good accordance with the + + 17 (PPh3) as a synthetic strategy on the reaction of compound 2 isolobal relation between H and Au because they share the 18 with equimolar amounts of [Au(CH3)(PPh3)] in refluxing acetone respective same position in these closely related molecular 19 resulted in the formation of the expected triangular cluster structures. 20 21 1. Introduction (PPh )}(η5-Cp)(CO) (μ-PPh )] could be realized using this path- 22 3 4 2 way. However the reaction principle was here successful only in 23 The isolobal relation between gold (I) cations [Au]+ and their the case of gold, not for the other coinage-metals copper and 24 complexes [AuL]+ on the one hand and protons [H]+ on the silver.[7] Moreover, Haupt and co-workers were successful inthe 25 other hand is well established in the literature. After the first preparation of dirhenium metal clusters containing two bridg- 26 general introduction of the isolobal analogy as a bridge ing M(PR ) fragments (M=Au, Ag).[8] In this context, in 2012, the 27 3 between inorganic, organometallic, and organic chemistry by chemistry of gold under the special consideration of the 28 Hoffmann,[1] only a few years later Stone highlighted the isolobality concept as a guide in the synthesis of metal clusters 29 importance of this concept in the field of the synthesis of bi- was reviewed by Raubenheimer and Schmidbaur.[9] Sometime 30 and multimetallic metal clusters also with particular consider- later Adams and co-workers described the isolobal relationship 31 ation of the isolobal relationship between the fragments H and between the molecules [Re (CO) (μ-H) ] and the cluster [Re {μ- 32 2 8 2 2 Au(PPh ).[2] In this context Braunstein and Rose[3] reviewed the Au(PPh )} (CO) ].[10] Both complexes can be regarded as 32- 33 3 3 2 8 synthesis, the bonding situation as well as the chemical and valence electron species and are formally unsaturated species. 34 catalytic reactivities of such bimetallic molecular clusters Recently we have reported the synthesis and structural 35 containing gold described at that time.[3] In 1985 the triangular characterization of new, doubly phosphanyl-bridged rhodium(II) 36 Rh Au cluster [Rh {μ-Au(PPh )}(μ-CO)(η5-Cp) (μ-dppm)]BF complexes of the formula [{Rh(η5-Cp)(μ-PPh )} ].[11] Closely 37 2 2 3 2 4 2 2 (dppm=Ph PCH PPh )[4] was reported even by the use of the related complexes of that type were already reported by Werner 38 2 2 2 isolobal relationship between the groups μ-H and μ-Au(L) as and co-workers,[12] and they were described as electron-rich 39 synthetic tool operating also in the case of a related silver species exhibiting strong metal basic properties which allow a 40 fragment.[5] Later, we also used this principle in our investiga- protonation of the RhÀ Rh bond. The molecular structure of this 41 tions and were successful in the preparation of Fe M clusters type of complex was confirmed at that time by the crystal- 42 2 (M=Cu, Ag, Au) using the complex [Fe (μ-CO)(CO) (μ-H)(μ-PR )] structure determination of the mixed phosphanido-bridged 43 2 6 2 (R=tBu) and the corresponding deprotonated species, species [Rh (η5-C Me ) (μ-PMe )(μ-PPh )].[13] Now we have also 44 2 5 5 2 2 2 respectively.[6] Even the synthesis of the metal cluster [Mo {μ-Au studied the protonation reaction of the RhÀ Rh bond in [{Rh(η5- 45 2 Cp)(μ-PPh )} ], affording the corresponding hydrido-bridged 46 2 2 [a] Prof. Dr. H.-C. Böttcher, Dr. M. Graf, Dr. P. Mayer cationic species which served as the precursor in the synthesis 47 Department Chemie of the isolobal-analogous Rh2Au cluster confirming the relation- 48 Ludwig-Maximilians-Universität München ship between H and Au(PPh ). On these findings we report in 49 Butenandtstraße 5–13, 81377 München (Germany) 3 E-mail: [email protected] this paper. 50 [b] Prof. Dr. M. Scheer 51 Institut für Anorganische Chemie 52 Universität Regensburg Universitätsstrasse 31, 93040 Regensburg (Germany) 2. Results and Discussion 53 © 2020 The Authors. Published by Wiley-VCH GmbH. This is an open access 54 article under the terms of the Creative Commons Attribution Non-Com- 5 The treatment of red solutions of [Rh2(η -Cp)2(μ-PPh2)2] (1) in 55 mercial NoDerivs License, which permits use and distribution in any med- diethyl ether with tetrafluoroboric acid at ambient temperature 56 ium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. resulted in a spontaneous reaction indicated by the quick 57 ChemistryOpen 2020, 9, 991–995 991 © 2020 The Authors. Published by Wiley-VCH GmbH Wiley VCH Montag, 05.10.2020 2010 / 179243 [S. 991/995] 1 Full Papers ChemistryOpen doi.org/10.1002/open.202000217 appearance of a dark red-brown precipitate (Scheme 1). After and high yield. An indication that the corresponding hydrido 1 being stirred for a short time, the product was separated by species was formed resulted mainly from the 1H NMR spectrum 2 filtration. The spectroscopic characterization by NMR methods of 2 showing a resonance signal in the high-field region as 3 (1H and 31P), elemental analysis, and mass spectrometry afforded triplet of triplets at δ= À 15.4 with the couplings 2J =20.0 Hz 4 PH unambiguously hints at the formation of the expected salt and J =20.0 Hz (CD Cl ). These data correspond very well 5 RhH 2 2 [Rh (η5-Cp) (μ-H)(μ-PPh ) ]BF (2) in an analytically pure form with the reported ones for [Rh (η5-Cp*) (μ-H)(μ-PMe ) ]PF (δ= 6 2 2 2 2 4 2 2 2 2 6 À 17.1, tt, 2J =34.0 Hz and J =22.0 Hz, CD NO ).[12] The 31P 7 PH RhH 3 2 {1H} NMR spectrum of 2 in CD Cl exhibited a signal at δ=120.3 8 2 2 as triplet (J = 98.3 Hz, compare to the former compound:[12] 9 RhP J =98.2 Hz). The starting compound 1 exhibited in its 31P{1H} 10 RhP NMR spectrum a triplet at δ=137.5 (J =144.5 Hz, CD Cl ).[11] 11 RhP 2 2 Finally, single crystals of 2 suitable for X-ray diffraction were 12 obtained and its molecular structure could be confirmed (see 13 below). To proof the isolobal principle between H and Au(PPh ), 14 3 we reacted equimolar amounts of 2 and [Au(CH )(PPh )] in 15 3 3 refluxing acetone. Successful preparations of gold-containing 16 clusters using this principle, partially under mild reaction 17 conditions, were already described in the literature.[3] During a 18 reaction period of 30 min, a color change of the solution 19 containing 2 and the gold component from red to red-brown 20 was observed. After removal of the solvent, crystals of a red- 21 brown product (3) were obtained from dichloromethane/ 22 dioxane, which were characterized by NMR spectroscopy (1H 23 and 31P), elemental analysis, and mass spectrometry. First 24 indications for the successful preparation of the isolobal 25 analogous Rh Au cluster complex cation resulted from the 31P 26 2 {1H} NMR spectrum of the isolated product. The latter exhibited 27 in its 31P{1H} NMR spectrum a signal in the downfield region as 28 doublet of triplets at δ =141.1 (J =112.1 Hz, 3J =11.0 Hz, 29 RhP PP CD Cl ) unambiguously indicating a coupling with a second 30 2 2 phosphorus atom. The signal of that nucleus was registered as 31 triplet of triplets at δ=58.2 with 2J =6.0 Hz (P on Au) and 32 RhP 3J =11.0 Hz. These values correspond well with reported 33 PP literature data of the compound [Rh {μ-Au(PPh )}(μ-CO)(η5- 34 2 3 Cp) (μ-dppm)]BF .[4] Also, the other spectroscopic data of the 35 2 4 product exhibited 3 as the triangular cluster compound [Rh {μ- 36 2 Au(PPh )}(η5-Cp) (μ-PPh ) ]BF (see Experimental Section). More- 37 3 2 2 2 4 over, single crystals of 3 suitable for X-ray diffraction were 38 obtained and the molecular structure could be confirmed (see 39 below).
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