| Abstract: | This dissertation describes the development of 2-guanidinobenzimidazole (GBI) containing ruthenium based organometallic hydrogen bond donors and their applications in second coordination sphere promoted catalysis (SCSPC). The synperiplanar triad arrangement of the NH donor (D) sites in GBI and derivatives are studied to establish that chelation preorganizes GBI in a DDD motif that is not an energy minimum with the free ligand. Laterhe importance of preorganization is explored in reactions catalyzed by GBI and derivatives. Protonated or methylated BAr[subscript f] (B(3,5-C₆H₃(CF₃)₂)₄) salts of GBI, 1⁺ BAr[subscript f]⁻ (84%) and 2⁺ BAr[subscript f]⁻ (58%), are prepared along with the protonated salts ofguanidine and 2-aminobenzimidazole, 3⁺ BAr[subscript f]⁻ (70% ) and 4⁺ BAr[subscript f]⁻ (75%),respectively. Refluxing GBI and ([eta]⁵-C₅H₅)Ru(PPh₃)₂(Cl) in toluene forms the chelatedcomplex [([eta]⁵-C₅H₅)Ru(PPh₃)(GBI)]⁺ Cl⁻ (8⁺ Cl⁻; 96%), which upon addition of CO forms [([eta]⁵-C₅H₅)Ru(CO)(GBI)]⁺ Cl⁻ (9⁺ C⁻; 91%). Subsequent anion metathesis of 8⁺ and 9⁺ Cl⁻ gives the respective PF₆⁻ and BAr[subscript f]⁻ salts (83-92%). 9⁺ PF₆⁻ can also beprepared from [([eta]⁵-C₅H₅)Ru(CO)(NCCH₃)₂]⁺ PF₆⁻ (81%). GBI and 9⁺ Cl⁻ (10 mol%,rt) are ineffective (48 h) for the condensations of 1-methylindole and trans-[beta]-nitrostyrene (6). In contrast, salts 1-4⁺ BAr[subscript f]⁻ (25-95%, 1 h) and 8-9⁺ X⁻ (PF₆⁻ andBAr[subscript f]⁻) are active catalysts (30-97%) under similar conditions. Furthermore, GBI derivatives with a NHR group (GBI-R; R = 16a, CH₂Ph; 16b, (S[subscript C])-CH(CH₃)Ph; 16c, (R[subscript C]R[subscript C])-CH-(CH₂)₄-CH-NMe₂; 16d, (R[subscript C]R[subscript C])-CH-(CH₂)₄-CH-NCH₂(CH₂)₃CH₂) are prepared. Reactions with [([eta]⁵-C₅H₅)Ru(CO)(NCCH₃)₂]⁺ PF₆⁻ afford the chiral-at-metal chelates [([eta]⁵-C₅H₅)Ru(CO)(GBI-R)]⁺ PF6₆⁻ (18a-d⁺ PF₆⁻, 39-77%). The Ru,C configurational diastereomers of 18c⁺ PF₆⁻ separate upon alumina chromatography (R[subscript Ru]R[subscript C]R[subscript C], >99:01 diastereomer ratio (dr); S[subscript Ru]R[subscript C]R[subscript C], <2:98 dr). Configurations are assigned by CD spectra, DFT calculations, and a crystal structure. Both (S[subscript Ru]R[subscript C]R[subscript C])-18c⁺ PF₆⁻ and (R[subscript Ru]R[subscript C]R[subscript C])-18c⁺ PF₆⁻ (1-10 mol%) catalyze Michael addition reactions between 1,3-dicarbonyl equivalents and 6 in high yields and enantioselectivities (90-99% ee). The free GBI-R ligand exhibits only modest activity. The chiral ruthenium center has little influence over the product configuration. Finally, ruthenium GBI complexes bearing a bulky electron withdrawing pentaphenylcyclopentadienyl ligand are accessed by treating a CH₃CN suspension of ([eta]⁵-C₅Ph₅)Ru(CO)₂(Br) with Me₃NO·2H₂O, GBI, and Ag⁺ PF₆⁻. Silica gelchromatography workups lead to [([eta]⁵-C₅Ph₅)Ru(CO)(GBI)]⁺ PF₆⁻ (48⁺ PF₆⁻; 70%),whereas with alumina [([eta]⁵-C₅Ph₅)Ru(CO)(GBI)]⁺ BAr[subscript f]⁻ (48+ BAr[subscript f]⁻; 69%) is obtainedafter anion metathesis. The neutral compound ([eta]⁵-C₅Ph₅)Ru(CO)(GBI_H) (49; 72%)bearing a deprotonated GBI ligand (GBI_H) is obtained from 48⁺ PF₆⁻ with K⁺ t-BuO⁻.These are characterized by NMR, other spectroscopic methods, and X-ray crystallography. Protonation of 49 with the axially chiral enantiopure phosphoric acid, (P)-Phos-H (HOP(=O)(o-C₁₀H₆O)₂)), leads to (R[subscript Ru]/S[subscript Ru])-48⁺ (P)-Phos⁻ (92%) as amixture of Ru,Axial configurational diastereomers. The diastereomer (S[subscript Ru])-48⁺ (P)-Phos⁻ (35%) can be isolated with >98:02 dr from cold toluene/hexane. Subsequent anion metathesis provides (S[subscript Ru])-48⁺ BAr[subscript f]⁻ (80%). The absolute configuration is assigned by CD spectroscopy. (S[subscript Ru])-48⁺ BAr[subscript f]⁻ (10 mol%) is an efficient catalyst for Friedel-Craftsalkylations and Michael addition reactions even under aerobic conditions. The addition of thiophenol to trans-3-cinnamoyloxazolidin-2-one is highly enantioselective (>99%). The neutral complex 49 is even capable of acting as a multifunctional catalyst and promotes Michael addition reaction of diethyl malonate and 6 in the absence of an external base. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155453 |
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