Copper Clusters Containing Hydrides in Trigonal Pyramidal Geometry

Abstract

Structurally precise copper hydrides [Cu 11 H 2 {S 2 P(O i Pr) 2 } 6 (C≡CR) 3 ], (R= Ph (1), C 6 H 4 F (2) and C 6 H 4 OMe (3) were first synthesized from the polyhydrido copper cluster [Cu 20 H 11 {S 2 P(O i Pr) 2 } 9 ] with nine equiv. of terminal alkynes. Later their isolated yields were significantly improved by direct synthesis from [Cu(CH 3 CN) 4 ](PF 6), [NH 4 ][S 2 P(O i Pr) 2 ], NaBH 4 , and alkynes along with NEt 3 in THF. 1, 2, and 3 were fully characterized by single-crystal X-ray diffraction, ESI-MS and multinuclear NMR spectroscopy. All three clusters have eleven copper atoms adopting 3, 3, 4, 4, 4-pentaccaped trigonal prismatic geometry, with two hydrides inside the Cu 11 cage, the position of which being ascertained by a single-crystal neutron diffraction structure of cluster 1 co-crystallized with a [Cu 7 (H){S 2 P(O i Pr) 2 } 6 ], 4 cluster. Six dithiophosphate and three alkynyl ligands stabilize the Cu 11 H 2 core in which the two hydrides adopt a trigonal pyramidal coordination mode. This coordination mode is so far unprecedented for hydride. The 1 H NMR resonance frequency of the two hydrides appears at 4.8 ppm, a value further confirmed 1 A c c e p t e d m a n u s c r i p t by 2 H NMR spectroscopy for their deuteride derivatives [Cu 11 (D) 2 {S 2 P(O i Pr) 2 } 6 (C≡CR) 3 ]. A DFT investigation allows understanding the bonding within this new type of copper(I) hydrides.

Reactivities of Interstitial Hydrides in a Cu11 Template: En Route to Bimetallic Clusters

“…This is the trace of as omewhat counterintuitive electron transfer from the cage 3d(Cu) AOsi nto the empty 5p p (Ag) ones, which largely overpasses the weak transfer from the hydrides to the 4s AOsofCu tri and (if any) Cu cap .T hus,the [M cent H 2 ] À identity of the encapsulated unit is less marked in 2' ' than in 1' '. Although larger by % 1ppm than the experimental hydride chemical shifts of Cu 11 H 2 , [9] 1 and 2 (4.89, 5.24 and 5.15 ppm, respectively), those computed in vacuum for Cu 11 H 2 ' ', 1' ' and 2' ' (5.9, 6.2 and 6.2 ppm, respectively) reflect their variation nicely.…”

“…Chemie precursor and 1 is that 1 has asupplementary Cu + ion inserted at the center of the pentacapped trigonal prism, thus right in the middle of the H•••H axis,d epicting al inear CuH 2 motif encapsulated within aCu 11 pentacapped triangular prism, the whole framework maintaining its D 3h ideal symmetry.Hence, the complete coordination environment of the two interstitial hydrides is now trigonal bipyramidal (m 5 -H), but with the averaged Cu top -H (1.92( 5) )a nd Cu tri -H (2.00( 5) )d istances being significantly larger than Cu cent -H (1.57( 5) ). When compared to their H 2 Cu 11 counterparts, [9] the Cu-Cu distances in 1 indicate that the insertion of one copper atom expands substantially the trigonal prismatic Cu 6 core.B eside of these differences,b oth H 2 Cu 11 and 1 have similar ligand environment, that is,s ix dtp ligands that cap Cu top -Cu tri -Cu tri -Cu cap butterflies through a( m 2 , m 2 )b inding mode and three triplybridging alkynyl groups (m 3 -h 1 )o nt he waist edge of the trigonal prism and one Cu cap atom. Thea lkynyl groups are inclined in such aw ay that the whole cluster symmetry is lowered to C 3h .…”

“…[12] Since these ligands are bridging the Cu cap and Cu ico atoms,their bite distance directly influences the Cu cap •••Cu ico distances,a nd by implication the Cu cap •••H distance.T he Ag cent -H-Cu tri and Cu tri -H-Cu tri angles in 2 (avg.97.4(5)8 8 and 118.3(5)8 8,respectively), also reflect the hydride trigonal pyramidal coordination mode.T othe best of our knowledge,t his is the first example of an eutron-characterized trigonal pyramidal hydride coordination mode in aA gCu 3 environment, coming right after that in aC u 4 environment, also proven to exist by neutron diffraction in H 2 Cu 11 . [9] It is worthwhile to mention that the trigonal pyramidal hydride coordination mode observed in 2 is one among several other m 4 -H possibilities. [1a, 7, 17] Finally,aq uestion that arises then is why,when treated with Cu + , H 2 Cu 11 leads to the formation of 1 (CuH 2 @Cu 11 ), whereas when treated with Ag + , 2 (AgH 2 @Cu 14 )i sf ormed.…”

“…[16] As depicted in Figure 1a,t he structure of 1 is strongly related to that of its H 2 Cu 11 precursor. [9] Thelatter template exhibits aC u 11 3,3,4,4,4-pentacapped trigonal prism with the two hydrides located inside the top and bottom Cu 4 tetrahedra (m 4 -H), in aposition closer to the prism triangular face,t hat is,i n at rigonal pyramidal coordination mode.T he whole H 2 Cu 11 framework has D 3h ideal symmetry.T he only significant difference between the H 2 Cu 11…”

“…At higher temperature,t he 31 PNMR spectrum of 1,w hich resonates at 99.5 ppm, shifts downfield to 100.4 ppm, which is the resonance frequency of [Cu 8 H{S 2 P(O i Pr) 2 } 6 ] + .Based on these observations,o ne can conclude that, at an elevated temperature (55 8 8C), cluster 1 is not as stable as its precursor template, H 2 Cu 11 . [9] In fact its purification is quite challenging. 1 decomposes into the starting H 2 Cu 11 template when passing through an aluminum oxide chromatography column.…”