Metal-Induced B–H Activation in Three-Component Reactions: 16-Electron Complex CpCo(S₂C₂B₁₀H₁₀), Ethyl Diazoacetate, and Alkynes

The three-component reactions of the 16-electron half-sandwich complex CpCo­(S₂C₂B₁₀H₁₀) (Cp = cyclopentadienyl) (<b>1</b>) with ethyl diazoacetate (EDA) and alkynes R₁R₂ (R₁ = Ph, R₂ = H; R₁ = CO₂Me, R₂ = H; R₁ = R₂ = CO₂Me; R₁ = Fc, R₂ = H) at ambient temperature lead to compounds CpCo­(S₂C₂B₁₀H₉)­(CH₂CO₂Et) ­(CHCO₂Et)­(R₁R₂) (<b>2</b>–<b>5</b>), CpCo­(S₂C₂B₁₀H₉)­(CH₂CO₂Et)­(R₂–R₁–CHCO₂Et) (<b>6</b>–<b>9</b>), CpCo­(S₂C₂B₁₀H₉)­(CH₂CO₂Et)­(CH­(Ph)­CCHCO₂Et) (<b>10</b>), and CpCo­(S₂C₂B₁₀H₉)­(CH₂CO₂Et)­(CH­(Fc)–CH–CCO₂Et) (<b>11</b>). In <b>2</b>–<b>5</b>, one alkyne is stereoselectively inserted into the Co–B bond, one EDA molecule is used to form a sulfide ylide, and the second EDA molecule is inserted into one Co–S bond to form a three-membered metallacyclic ring. At ambient temperature <b>2</b>–<b>5</b> undergo rearrangement to <b>6</b>–<b>9</b> through migratory insertion of the inserted EDA. Different from <b>2</b>–<b>5</b>, in <b>10</b> phenylacetylene is inserted into the Co–B bond at the terminal carbon and the terminal carbon is coupled with one EDA to afford a six-membered metallacyclic ring with the CO coordination to metal. In <b>11</b>, a stable Co–B bond is generated, and one EDA and one ethynylferrocene are inserted into the Co–S bond. Moreover, if weakly basic silica is present, <b>2</b>–<b>4</b> can lose an apex BH close to the two carbon atoms of <i>o</i>-carborane to give rise to CpCo­(S₂C₂B₉H₉)­(CH₂CO₂Et)₂­(R₁R₂) (<b>12</b>–<b>14</b>) accompanied by the coordination of the two sulfide ylide units to the metal center. The solid-state structures of <b>2</b>–<b>4</b>, <b>6</b>–<b>12</b>, and <b>14</b> were characterized by X-ray structural analysis

Pyrrolylmethyl Functionalized <i>o</i>‑Carborane Derivatives

The reactions of the 16e half-sandwich complex CpCoS₂C₂B₁₀H₁₀ (<b>1</b>), diazo esters, and various 1,6-diynes (<b>3a</b>–<b>i</b>; PhN­(CH₂CCH)₂, 4-Me-PhN­(CH₂CCH)₂, 4-OMe-PhN­(CH₂CCH)₂, 4-F-PhN­(CH₂CCH)₂, BzN­(CH₂CCH)₂, O­(CH₂CCH)₂, C­(Ac)₂(CH₂CCH)₂, N­(CH₂CCH)₃, NH­(CH₂CCH)­N­(CH₂CCH)₂) were investigated, in which two novel types of B–H activated products CpCoS₂B₁₀H₉(CH₂CO₂Et)­C₅H₃N­(R)­(CHCHCO₂Et) (<b>4a</b>–<b>c</b>; R = Ph, 4-Me-Ph, 4-OMe-Ph) and the key intermediate CpCoS₂B₁₀H₉(CHCO₂Me) (CH₂CO₂Me) (<b>9</b>) were isolated. <b>9</b> features a reactive Co–B bond, which triggers insertion of various 1,6-diynes to further lead to different final products. Substrates <b>3a</b>–<b>c</b> are activated by the Co–B bond to produce <i>o</i>-carborane derivatives <b>4a</b>–<b>c</b> which are functionalized by a cobalt-complexed η³-pyrrolylmethyl group. The pyrrole ring is formed by in situ ring closure of 1,6-diynes. Control experiments and isolation of the intermediate CpCoS₂B₁₀H₉(CHCO₂Me)­(CH₂CO₂Me)­HCCCH₂N­(4-Me-Ph)­(CH₂CCH) (<b>10</b>) support the proposed mechanism concerning the formation of <b>4a</b>–<b>c</b> analogues by oxidation. All of the new complexes were characterized by NMR, IR, elemental analysis, and mass spectrometry. The structures of <b>4a</b>–<b>6a</b> and <b>9</b> were determined by single-crystal X-ray diffraction analysis as well

Relative expression of <i>BpMADS</i> in birch.

<p>Young leaves and inflorescences of birch treated with 6 h of light or 6 h of dark. Values are expressed as mean ± S.D. (n = 3 samples for each test).</p

Subcellular localization analysis of <i>BpMADS</i>.

<p>The <i>BpMADS-GFP</i> fusion (and <i>GFP</i> alone) were transiently expressed under the control of the CaMV 35S promoter in onion epidermal cells and observed under a confocal microscope. The photographs were taken in dark field for green fluorescence localization (A, D), in bright light to examine cellular morphology (B, E), and in combination (C, F). (A, B, C) Transient expression of GFP in the control (D, E, F) Expression of the BpMADS-GFP fusion protein.</p

Starch-iodine staining of leaves.

<p>After 3 h of culture under normal light conditions, the leaves were removed from the plants and subjected to starch-iodine staining analysis.</p

Microscopic observation of tobacco.

<p>(A) The fourth true leaves from 25-day-old wild-type and 35S::BpMADS seedlings. (B, C) SEM observation of upper-epidermal cells in the third true leaves of 20-day-old wild-type (B) and 35S::BpMADS (C) seedlings; arrows indicate immature guard cells. (D, E) SEM observation of cross sections of third true leaves from 20-day-old wild-type (D) and 35S::BpMADS (E) seedlings. (F, G) Hand-cut sections of 4-week-old wild-type (F) and 35S::BpMADS (G) tobacco stems treated with phloroglucinol-HCl for lignin staining. (H, I) Histological observation of apical shoots from 15-day-old wild-type (H) and 35S::BpMADS (I) tobacco seedlings.</p

Grafting experiment.

<p>(A) The wild-type (left) and 35S::BpMADS stock+wild-type scion (right) plants were in the flowering stage. (B, C) 90-day-old plants (B) and a close-up view near the base of each stem (C). 1, 35S::BpMADS; 2, wild-type stock +35S::BpMADS scion; 3, wild-type; 4, 35S::BpMADS stock+wild-type scion.</p

Primers employed in quantitative real-time PCR.

<p>Primers employed in quantitative real-time PCR.</p

Relative expression levels of flowering-related genes.

<p>35S::BpMADS plants showed significant differences in the relative expression levels of flowering-related genes compared with the wild-type, as determined by SPSS 11.5 analysis using Student's t-test (p<0.01). Values are expressed as means (n  = 3); error bars denote S.D. M3, <i>NsMADS3</i>; M4, <i>NtMADS4</i>; M5, <i>NtMADS5</i>; M11, <i>NtMADS11</i>; NFL2, <i>NFL2</i>; FUL, <i>NtFUL</i>; SOC1, <i>NtSOC1</i> were induced in transgenic plants.</p

TEM observation of chloroplasts.

<p>For TEM observation of chloroplasts, second true leaves were collect from 14-day-old tobacco plants. (A) wild-type; (B) 35S::BpMADS line MADS-1. UE, upper-epidermis; PM, palisade mesophyll; SM, spongy mesophyll; LE, lower-epidermis. Arrows indicate chloroplasts.</p