According to the following cycle diagram, which of the following statements is correct:

<MultiModal>![This is a catalytic reaction cycle diagram, in which RCCC(=O)[Co](C=O)(C=O)C=O reacts with hydrogen to produce unknown substance A; A then generates [CoH](C=O)(C=O)C=O and RCCC=O; [CoH](C=O)(C=O)C=O can undergo an addition reaction with olefins, with the double bond coordinating to the cobalt atom; subsequently, the coordinated olefin inserts into the cobalt-hydrogen bond; then, the carbon end of carbon monoxide coordinates to cobalt, and then, through a one-step insertion, RCCC(=O)[Co](C=O)(C=O)C=O is regenerated, completing the cycle](/media/uploads/a92adc9f-3c77-4911-b348-658fcf7c1306.png)</MultiModal>
根据如下循环示意图，下列说法正确的是:

<MultiModal>![这是一个催化反应循环图，其中RCCC(=O)[Co](C=O)(C=O)C=O与氢气反应，生成未知物质A；A随后生成[CoH](C=O)(C=O)C=O和RCCC=O；[CoH](C=O)(C=O)C=O可与烯烃发生加成反应，双键对钴原子配位；随后配位的烯烃插入钴氢键；然后一氧化碳碳端对钴配位，再通过一步插入，重新生成RCCC(=O)[Co](C=O)(C=O)C=O，完成循环](/media/uploads/a92adc9f-3c77-4911-b348-658fcf7c1306.png)</MultiModal>
The coordination number of cobalt in substance $A$ is $4$.
The central atom of substance $A$ does not obey the 18-electron rule.
The oxidation state of cobalt in substance A is +3.
$A$ contains $3$ carbonyl groups.
Oxidative addition yields product $A$ where only one hydrogen atom is bonded to cobalt.
Both B and C above are correct.
物质$A$中钴的配位数为$4$
物质$A$的中心原子不符合$18$电子规则
物质$A$中钴的氧化态为$+3$
$A$中有$3$个羰基
氧化加成得到生成物$A$里，只有一个氢原子连接在钴上
以上B和C都正确
This reaction is a typical oxidative addition-reductive elimination mechanism, involving the change in valence of the central cobalt atom. The first step is the cleavage of the hydrogen chemical bond, followed by an addition reaction. The addition site may be the cobalt atom, the carbonyl group, or the coordinated carbon monoxide. Based on the cobalt-hydrogen bond in the product after the decomposition of $A$, it is inferred that the addition occurs on the cobalt.
$A$ is [Co](H)(H)(C#O)(C#O)(C#O)(C(=O)R.

<Checkpoint>[$A$ is [Co](H)(H)(C#O)(C#O)(C#O)(C(=O)R)](1)</Checkpoint>

For option **A**, the coordination number of the cobalt atom is $6$;

<Checkpoint>[The coordination number of the cobalt atom is $6$](0.5)</Checkpoint>

For option **B**, the cobalt atom has $9$ valence electrons, and the ligands provide a total of $9$ electrons, which conforms to the $18$-electron rule;

<Checkpoint>[The cobalt atom has $9$ valence electrons, and the ligands provide a total of $9$ electrons, which conforms to the $18$-electron rule](1)</Checkpoint>

For option **C**, the oxidation state of the cobalt atom is $+3$;

<Checkpoint>[The oxidation state of the cobalt atom is $+3$](0.5)</Checkpoint>

For option **D**, there are $4$ carbonyl groups in $A$;

<Checkpoint>[There are $4$ carbonyl groups in $A$](0.5)</Checkpoint>

For option **E**, the hydrogen molecule breaks its bond, and both hydrogen atoms are added to the cobalt.

<Checkpoint>[The hydrogen molecule breaks its bond, and both hydrogen atoms are added to the cobalt](0.5)</Checkpoint>

In summary, **C** is correct.
本反应是典型的氧化加成-还原消除机理，涉及中心钴原子的变价，第一步氢气化学键断裂，发生加成反应，加成的位点可能是钴原子，羰基，配位的一氧化碳。根据$A$分解后的产物有钴氢键，推断加成在钴上。
$A$为[Co](H)(H)(C#O)(C#O)(C#O)(C(=O)R。

<Checkpoint>[$A$是[Co](H)(H)(C#O)(C#O)(C#O)(C(=O)R)](1)</Checkpoint>

对于**A**选项，钴原子的配位数为$6$；

<Checkpoint>[钴原子的配位数为$6$](0.5)</Checkpoint>

对于**B**选项，钴原子有$9$个价电子，配体共提供$9$个电子，符合$18$电子规则；

<Checkpoint>[钴原子有$9$个价电子，配体共提供$9$个电子，符合$18$电子规则](1)</Checkpoint>

对于**C**选项，钴原子氧化态为$+3$；

<Checkpoint>[钴原子氧化态为$+3$](0.5)</Checkpoint>

对于**D**选项，$A$中有$4$个羰基；

<Checkpoint>[$A$中有$4$个羰基](0.5)</Checkpoint>

对于**E**选项，氢气分子断键，两个氢原子均加成到钴上。

<Checkpoint>[氢气分子断键，两个氢原子均加成到钴上](0.5)</Checkpoint>

综上所述，**C**正确。