Reaction of 2‐Butyne with nido ‐[1,2‐(Cp*RuH) ₂ B ₃ H ₇ ]: Improved Kinetic Control Leads to Metallacarboranes of Novel Composition and Structure

Abstract

The conventional route to metallacarboranes proceeds in a sequence of steps leading from polyborane to carborane to metallacarborane. [1±4] Although a fruitful strategy, it is also one in which strong bonds are formed before weak ones. Access to more diverse chemistry might arise by adoption of the reverse strategy, that is, formation of BÀB/BÀM before B À C/M À C bonds, thereby generating the most stable products quenched with 10 % perchloric acid (10 ml) and then extracted with CH 2 Cl 2 . The solvent was evaporated under reduced pressure, and the residue was washed with MeOH and then recrystallized from EtOH/Et 2 O to give colorless crystals of 3 (1.36 g, 66 % yield), m.p. 175 ± 176 8C. 1 H NMR (400 MHz, CD 3 CN): d 5.08 (s, 1 H), 7.59 ± 7.64 (m, 8 H), 7.69 ± 7.74 (m, 4 H), 8.02 ± 8.06 ppm (m, 8 H); 13 C NMR (100 MHz, CD 3 CN): d 49.3, 127.9, 131.0, 135.2, 140.8 ppm; IR (KBr): n Ä 3315, 3269, 3094, 3062, 1095 cm À1 ; elemental analysis calcd for C 25 H 23 ClN 2 O 4 S 2 : C 58.30, H 4.50, N 5.44; found: C 58.29, H 4.46, N, 5.46. 5:A mixture of 4 (414 mg, 1.0 mmol) and methyl iodide (187 mL, 3 mmol) in acetonitrile (10 mL) was stirred at room temperature for 1 h. A solution of sodium perchlorate (184 mg, 1.5 mmol) in acetonitrile (10 mL) was added, and then the solvent was evaporated under reduced pressure. The residue was dissolved in water (10 mL) and extracted with CH 2 Cl 2 . After removal of the solvent, the residue was purified by recrystallization from MeOH/Et 2 O to afford 5 as colorless crystals (152 mg), [7] m.p. 184 ± 185 8C.

Reaction of nido-1,2-(Cp∗RuH)2B3H7 with ethynylferrocene to yield new metallacarboranes

“…Heating up to 80°C leads to decomposition rather than conversion from one to the other confirming the existence of a substantial barrier to interconversion. The two isomers are analogous to the clusters A and B generated from the methyl propiolate reaction [15] and shown in Scheme 1 as C is the analog of the antiMarkovnikoff addition of the alkyne. Based on our interpretation of the conversion of A and B to C-O inserted products, the barrier to isomer conversion in this system is lower than that for 2 and 3.…”

“…It was observed that a metal plays a critical role. For example, the dirhodaborane leads predominantly to catalytic cyclotrimerization of alkynes [10,11]; the diiridaborane needs a molybdenum center to promote alkyne insertion [12]; and the diruthenaborane, nido-1,2-(Cp * RuH) 2 B 3 H 7 (1) leads to diverse, unprecedented products even at ambient temperature.…”

“…If pushed, some undergo further conversions [13][14][15][16][17]. Relative to internal alkynes, terminal ones create novel compounds, e.g., the first M-B alkylidene complexes generated from cooperative reactivities of metal hydrides and boron hydrides of 1.…”

Metallaborane reaction chemistry. Part 10. Phenylacetylene incorporation via [4,4-(PMe2Ph)2-arachno-4-PtCB8H12] in a ‘converse’ metalladicarbaborane synthesis of [7,7-(PMe2Ph)2-isonido-7,6,8-PtC2B6H7-6-Ph]

“…More recently, we and others became interested in these types of Ôconverse reactionsÕ of acetylenes with boron-containing clusters, using both metallaborane and heteroborane substrates [5][6][7][8][9][10][11]. It was found, for example, that the incorporation of HC"CH into the arachno nine-vertex [4,4,4,4-(CO)(PPh 3 ) 2 H-4-IrB 8 H 12 ] cluster gives an 11-vertex {IrC 2 B 8 } species, and that HC"CAC(Me)@CH 2 gives both 10-vertex {IrCB 8 } and 11-vertex {IrC 2 B 8 } species [7,8].…”

“…Of the few examples, it had been shown that addition of alkynes, accompanied by boron-vertex loss, to [2-(C 5 H 5 )-nido-2-CoB 4 H 8 ] gives [1-(C 5 H 5 )-nido-1,2,3-CoC 2 B 3 H 7 ] and Csubstituted derivatives [3], and that the addition of MeC"CMe into [1,1,1-(CO) 3 [4]. More recently, we and others became interested in these types of Ôconverse reactionsÕ of acetylenes with boron-containing clusters, using both metallaborane and heteroborane substrates [5][6][7][8][9][10][11]. It was found, for example, that the incorporation of HC"CH into the arachno nine-vertex [4,4,4,4- [7,8].…”